United States v. Rodney Flucas ( 2022 )


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  •                 FOR PUBLICATION
    UNITED STATES COURT OF APPEALS
    FOR THE NINTH CIRCUIT
    UNITED STATES OF AMERICA,                Nos. 19-10065
    Plaintiff-Appellee,           19-10420
    v.                          D.C. No.
    2:17-cr-00209-
    RODNEY FLUCAS, AKA Rodney J.                 KJM-1
    Flucas, AKA Rodney Rochea
    Flucas, AKA Rodney Rochen
    Flucas,                                    OPINION
    Defendant-Appellant.
    Appeal from the United States District Court
    for the Eastern District of California
    Kimberly J. Mueller, Chief District Judge, Presiding
    Argued and Submitted September 3, 2021
    San Francisco, California
    Filed January 21, 2022
    Before: Mary M. Schroeder, Johnnie B. Rawlinson, and
    Jay S. Bybee, Circuit Judges.
    Opinion by Judge Rawlinson;
    Concurrence by Judge Schroeder;
    Dissent by Judge Bybee
    2                   UNITED STATES V. FLUCAS
    SUMMARY*
    Criminal
    The panel affirmed convictions for transportation of a
    minor with intent to engage in criminal sexual activity in
    violation of 
    18 U.S.C. § 2423
    (a), and transportation of an
    individual with intent to engage in criminal sexual activity in
    violation of 
    18 U.S.C. § 2421
    (a).
    The defendant contended that he is entitled to a new trial
    because the district court erroneously instructed the jury
    concerning the requisite intent for transporting an individual
    or minor for criminal sexual activity in violation of §§ 2421
    or 2423. He maintained that the district court improperly
    instructed the jury that he could be convicted if criminal
    sexual activity was a motivating purpose of the transportation
    of an individual, and that the district court was required to
    instruct the jury that criminal sexual activity must be the
    dominant purpose in order to establish the requisite intent.
    The panel held that the district court did not abuse its
    discretion in instructing the jury, consistent with this court’s
    precedent, that the government was required to prove beyond
    a reasonable doubt that a dominant, significant, or motivating
    purpose of the transportation of the defendant’s victims was
    to engage in criminal sexual activity. The panel wrote that
    the non-retroactive amendment to 
    18 U.S.C. § 2423
    (b), a
    statute under which the defendant was not charged, does not
    undermine the consistent precedent throughout the circuits
    *
    This summary constitutes no part of the opinion of the court. It has
    been prepared by court staff for the convenience of the reader.
    UNITED STATES V. FLUCAS                       3
    rejecting the “dominant purpose” mens rea advocated by the
    defendant.
    The panel addressed the defendant’s additional challenges
    to his convictions in a concurrently filed memorandum
    disposition.
    Concurring, Judge Schroeder wrote to underscore key
    points that in her view undermine the dissent: (1) the dissent
    views as binding language the Supreme Court used more than
    seventy years ago in a case that raised different issues;
    (2) courts have routinely treated “motivating” and
    “significant” as interchangeable; and (3) one cannot assume
    that the addition of “or motivating” to the instruction was
    responsible for a second jury convicting after the first jury did
    not.
    Dissenting, Judge Bybee wrote that no court has
    considered whether “a motivating purpose” is different from
    “a dominating or significant purpose,” and that in his view,
    those terms are not synonymous. He wrote that the
    instruction lowered the government’s burden of proof,
    contrary to the holding in Mortensen v. United States,
    
    322 U.S. 309
     (1944), and this court’s Mann Act decisions;
    and that the error is not harmless beyond a reasonable doubt.
    4                 UNITED STATES V. FLUCAS
    COUNSEL
    Brian C. McComas (argued), Law Office of B.C. McComas
    LLP, San Francisco, California, for Defendant-Appellant.
    Veronica M.A. Alegria (argued), Assistant United States
    Attorney; Camil A. Skipper, Appellate Chief; Phillip A.
    Talbert, Acting United States Attorney; United States
    Attorney’s Office, Sacramento, California; for Plaintiff-
    Appellee.
    OPINION
    RAWLINSON, Circuit Judge:
    Rodney Flucas (Flucas) appeals his convictions for
    transportation of a minor with intent to engage in criminal
    sexual activity in violation of 
    18 U.S.C. § 2423
    (a), and
    transportation of an individual with intent to engage in
    criminal sexual activity in violation of 
    18 U.S.C. § 2421
    (a).
    The evidence presented during a jury trial demonstrated that
    Flucas sexually abused his daughters and other minors in his
    household over several years, and was the father of numerous
    children from his own daughters. The issue that confronts us
    in this appeal is whether the district court properly instructed
    the jury that it could convict Flucas if a motivating purpose
    of his transportation of his victims from Oregon to California
    was to engage in criminal sexual activity. Flucas maintains
    that the district court was required to instruct the jury that the
    government must prove beyond a reasonable doubt that the
    dominant purpose of his transportation of his sexual abuse
    victims was to engage in criminal sexual activity. Flucas
    asserts that he was entitled to this instruction in support of his
    UNITED STATES V. FLUCAS                           5
    theory of defense that the dominant purpose of his
    transportation of his victims from Oregon to California was
    to obtain a higher paying job, not to engage in criminal sexual
    activity.
    We have jurisdiction pursuant to 
    28 U.S.C. § 1291
    , and
    we affirm Flucas’ convictions. We hold that the district court
    did not abuse its discretion in instructing the jury, consistent
    with our precedent, that the government was required to
    prove beyond a reasonable doubt that a dominant, significant,
    or motivating purpose of the transportation of Flucas’ victims
    was to engage in criminal sexual activity.1
    I. BACKGROUND
    In a third superseding indictment, Flucas was charged
    with “knowingly transport[ing] in interstate commerce and
    foreign commerce individuals Person 1, Person 2, and Person
    3, each of whom had not attained the age of 18 years, with
    intent that each such individual engage in sexual activity for
    which any person could be charged with a criminal offense”
    in violation of 
    18 U.S.C. § 2423
    (a). The indictment alleged
    that Flucas engaged in incest, sexual intercourse, and oral
    copulation with Person 1, Person 2, and Person 3 in violation
    of California law. Flucas was also charged under 
    18 U.S.C. § 2421
    (a) with “knowingly transport[ing] in interstate
    commerce and foreign commerce an individual, Person 4,
    with intent that such individual engage in sexual activity for
    1
    In a memorandum disposition filed concurrently with this opinion,
    we address Flucas’ additional challenges to his convictions.
    6                   UNITED STATES V. FLUCAS
    which any person could be charged with a criminal offense,
    to wit: incest in violation of California Penal Code § 285.”2
    During Flucas’ second trial,3 Person 1 testified that, in
    2014, she met Person 2, Flucas’ daughter, in Oregon, and
    started living at Flucas’ residence. Person 1 stated that Flucas
    was the father of her son, who was born in Stockton,
    California, when Person 1 was sixteen years old. Person 1
    related that Flucas started to “touch [her] in a sexual manner”
    when she was fifteen years old, and had intercourse with her
    between one and three times a week. Flucas instructed
    Person 1 not to tell anyone about the sex acts, and to fabricate
    a name for the father of her child.
    Flucas told Person 1 that he wanted her to move with him
    to California in 2015 because she “was having his child.”
    Flucas threatened Person 1, that if she attempted to stay in
    Oregon with her father or stepmother, he would “bring [her]
    back” to him. Person 1 did not believe that she “had a choice
    about moving” to California. Person 1 testified that Flucas
    continued to have intercourse “[a] few times a week” with her
    in California. Person 1 did not believe that she “could stop
    what was happening to [her].”
    Person 2, Flucas’ daughter, testified that Flucas started to
    have intercourse with her when she was thirteen years old.
    Person 2 became pregnant with Flucas’ child in 2013, when
    2
    A third count alleging that Flucas transported Person 2 and Person
    3 with intent to engage in criminal sexual activity, was dismissed.
    3
    In Flucas’ first trial, the jury convicted Flucas of attempted witness
    tampering, but was unable to reach a verdict on the transportation
    offenses.
    UNITED STATES V. FLUCAS                      7
    she was fifteen years old, but lost the child. During an
    investigation by child protective services, Person 2 did not
    disclose the sexual abuse or that Flucas was the father of her
    child. Prior to her interview, Flucas warned Person 2 that she
    knew “what and what not to say.”
    Person 2 testified that she moved with Flucas to Klamath
    Falls, Oregon, when she was fifteen years old, after he lost his
    job in Americus, Georgia, due to allegations by “her little
    sisters’ and brothers’ grandmother” of sexual abuse. They
    relocated to Oregon because Flucas was “trying to move
    away from . . . the people who were [making] the
    allegations.” Person 2 related that Flucas continued to
    sexually abuse her in Oregon.
    In 2017, Person 2 realized that she was unable to protect
    her sisters, and decided that she “didn’t want to live
    anymore.” Person 2 attempted to commit suicide by crashing
    her car into a pole. At the hospital, Person 2 informed law
    enforcement about the sexual abuse.
    Person 3, Flucas’ daughter, testified that Flucas started to
    sexually abuse her when she was six years old, and had
    intercourse with her for the first time when she was thirteen
    years old. Flucas promised that he would purchase a cell
    phone, computer, and car if she had intercourse with him.
    Person 3 confirmed that Flucas continued to have intercourse
    with her after moving to Oregon and California.
    Person 3 related that in 2017 she attempted to commit
    suicide with “a bunch of [Flucas’] narcotics” because she
    “didn’t want to be [in his house] anymore.” Person 3 testified
    that she slept for most of the day until Flucas returned home.
    Person 3 stated that, when Flucas returned, he took her into
    8                UNITED STATES V. FLUCAS
    a closet in his bedroom, where she vomited and they “had
    sex.” When Person 3 was interviewed by child protective
    services, Flucas told her to deny any sexual abuse.
    Person 4, Flucas’ daughter, testified that Flucas was the
    father of her three children. Person 4 related that, in August,
    2008, she was living with Flucas in Valdosta, Georgia. In
    February, 2010, Flucas started to touch Person 4 “in a sexual
    manner,” when she was in the ninth grade. Person 4 testified
    that she was fifteen when Flucas began having intercourse
    with her. Person 4 related that she was “confused,” and
    became physically attracted to her father because he “made
    [her] believe that [she] was the only one he wanted and . . . he
    could take care of [her] and [her] kids.” Person 4 told her
    sisters about the sexual abuse, but Flucas convinced them that
    she was lying. Person 4 subsequently “covered up” her story
    at Flucas’ insistence. Flucas also told Person 4 that he had
    “recordings in the phones and cameras in the rooms to see
    what you all are doing,” and commanded that “[w]hat
    happens in this house stays in this house.”
    When Person 4 gave birth to her first child, Flucas told
    her to fabricate the name of a father. Flucas also instructed
    her not to provide the name of a father on the child’s birth
    certificate. According to Person 4, Flucas told her that he
    wanted to have “seven more kids” with her, and was angry
    when she attempted to use birth control.
    In April, 2014, Person 4 was interviewed by the Georgia
    Department of Family and Children’s Services. Person 4 lied
    to the investigators when she told them that Flucas did not
    sexually abuse her. Person 4 related that she subsequently
    moved with Flucas and other members of his household to
    Americus, Georgia, where they resided for approximately one
    UNITED STATES V. FLUCAS                    9
    month. Person 4 testified that it was Flucas’ idea to move to
    Americus, and that he continued to have intercourse with her.
    Flucas was eventually fired from his job in Americus,
    Georgia, when his employer was informed about sexual abuse
    allegations. Flucas, Person 4, Person 4’s two children, Person
    3, Person 2, and other members of the household
    subsequently moved to Klamath Falls, Oregon, in September,
    2014. Person 4 testified that Flucas would not allow her to
    contact her mother to inform her where she was residing.
    While in Oregon, Person 4 became pregnant with her third
    child.
    Person 4 related that, in August, 2015, Flucas decided to
    move to Stockton, California. Flucas prohibited Person 4
    from contacting her mother. Flucas continued to have
    intercourse with Person 4 in California. Flucas also told her
    that, if she ever married, she “still [had to] have sex with
    him.”
    Person 4 related that, after Person 2 was involved in an
    accident, Flucas threatened Person 4 that, “If I go down you
    go down. For every child you have, there’s like a three-year
    sentence.” Person 4 was interviewed by a detective after
    Person 2’s accident, and was confronted with DNA results
    indicating that Flucas was the father of her children. As
    directed by Flucas, Person 4 told the detective that she
    “inseminated [herself] with a syringe” with semen from his
    condoms.
    Person 4 testified that Flucas had intercourse with her on
    October 28, 2017, at a hotel in California. According to
    Person 4, Flucas told her that they could move to Switzerland,
    Rhode Island, or New Jersey, where incest was legal.
    10                  UNITED STATES V. FLUCAS
    Person 5 testified that her mother was in a relationship
    with Flucas, and that Flucas sexually abused Person 5 when
    she was eight years old. Flucas had intercourse with Person
    5 for the first time when she was thirteen years old. Flucas
    told Person 5 that she was “his soulmate,” and that, “if [she]
    cheated on him, he’d kill [her].” Person 5 explained that she
    was unable to tell anyone about the sexual abuse because she
    didn’t think she would be believed. Person 5 eventually
    thought she was “in love” with Flucas.
    Person 5 testified that Flucas was the father of her six
    children. Flucas instructed Person 5 to fabricate the name of
    a father for the children. Flucas also told Person 5 that he
    wanted to have between eight and ten children with her.
    Person 5 moved with Flucas to Oregon in March, 2015,
    when she was “eight or nine months pregnant.” Person 5
    testified that Flucas continued to have intercourse with her in
    Oregon. When they subsequently moved to Stockton,
    California, Flucas prohibited Person 5 from informing her
    mother. Flucas continued to have intercourse with Person 5
    in California, and Person 5 became pregnant.
    When Person 5 was interviewed by a detective, she was
    presented with DNA results indicating that Flucas was the
    father of her children. Person 5 told the detective that she
    inseminated herself with Flucas’ sperm because “that’s the
    story that Mr. Flucas told [her] to say.”4
    4
    The dissent characterizes the evidence of Flucas’ guilty as “flimsy.”
    Dissenting Opinion, p. 66. The dissent bases this characterization on
    Flucas’ testimony that he moved to California for a better paying job. See
    id. at 66. But this characterization does not acknowledge powerful
    testimony from the victims detailing Flucas’ controlling behavior, his
    UNITED STATES V. FLUCAS                            11
    Flucas testified that he had intercourse with Person 4, his
    daughter, and acknowledged that sexual abuse occurred while
    residing in Georgia. However, Flucas maintained that he
    moved to California to seek a better paying job. Flucas’
    defense was that he moved for financial reasons, not to
    transport his daughters and the other minors for criminal
    sexual activity.
    At trial, the government proposed the following
    instruction with respect to the intent requirements for a
    conviction under 
    18 U.S.C. § 2421
     and 
    18 U.S.C. § 2423
    :
    To find the defendant guilty of Count One
    and/or Count Two, you need not find that the
    intended criminal sexual activity was the
    defendant’s sole or most important purpose.
    It is sufficient if the government proves
    beyond a reasonable doubt that the sexual
    activity was a significant, dominant, or
    motivating purpose. In other words, the
    government must prove that the criminal
    sexual activity was not merely incidental to
    the transportation. A person may have more
    than one significant, dominant, or motivating
    purpose for transporting others across a state
    line.
    The government proposed the instruction because the jury in
    Flucas’ first trial “struggled with the intent instruction and
    asked for further clarifying instructions,” and the proffered
    travels from other states where he was under investigation, and his refusal
    to allow his victims to notify their relatives that they had moved.
    12                   UNITED STATES V. FLUCAS
    instruction “added clarity about the nature of the intent
    instruction.”5
    Flucas objected to the proposed instruction because “it
    [was] not sufficient for the government to prove that illegal
    sexual activity was a motivating purpose,” and proposed an
    alternative instruction:
    It is not necessary for the government to prove
    that the (prostitution or) illegal sexual activity
    was the sole purpose for any transportation
    from one state to another. A person may have
    several different purposes or motives for such
    travel and each may prompt in varying
    degrees the act of making the journey. The
    government must prove beyond a reasonable
    doubt, however, that a significant or dominant
    purpose of the travel from one state to another
    was to have the person(s) transported engage
    in (prostitution or) illegal sexual activity.
    The Government must prove that the criminal
    sexual activity was not merely incidental to
    the transportation.
    The district court determined that use of the term
    “motivating” was consistent with legal precedent, and
    instructed the jury that:
    5
    During Flucas’ first trial, the jury asked the district court to “clarify
    the court’s definition of intent, beyond the instructions given.”
    UNITED STATES V. FLUCAS                           13
    To find the defendant, Mr. Flucas, guilty of
    Count 1 and/or Count 2, you need not find
    that the intended criminal sexual activity was
    the defendant’s sole or most important
    purpose.
    It is sufficient if the government proves
    beyond a reasonable doubt that the sexual
    activity was a significant, dominant or
    motivating purpose.
    In other words, the government must prove
    that the criminal sexual activity was not
    merely incidental to the transportation.
    A person may have more than one significant
    dominant or motivating purpose for
    transporting others across a state line. To find
    Mr. Flucas guilty of Counts 1 and/or 2, the
    government must prove that Mr. Flucas
    intended Person 1, 2, 3 and/or 4 to engage in
    criminal sexual activity after transporting
    them from one state to another state, not that
    anyone actually engaged in such conduct.6
    6
    The dissent’s speculative assertion that “we must assume that [the
    jury] chose the common denominator – ‘motivating’ – because satisfying
    that standard would automatically satisfy the higher standards of
    ‘dominant’ and ‘significant’” is accompanied by no supporting authority.
    Dissenting Opinion, p. 65.
    14                  UNITED STATES V. FLUCAS
    The jury found Flucas guilty, and the district court
    imposed a life sentence. Flucas filed a timely notice of
    appeal.7
    II. STANDARDS OF REVIEW
    “We review the formulation of jury instructions for abuse
    of discretion, but review de novo whether those instructions
    correctly state the elements of the offense and adequately
    cover the defendant’s theory of the case. . . .” United States
    v. Koziol, 
    993 F.3d 1160
    , 1179 (9th Cir. 2021) (citation and
    internal quotation marks omitted).
    III.       DISCUSSION
    Flucas contends that he is entitled to a new trial because
    the district court erroneously instructed the jury concerning
    the requisite intent for transporting an individual or minor for
    criminal sexual activity in violation of 
    18 U.S.C. § 2421
     and
    
    18 U.S.C. § 2423
    . Flucas maintains that the district court
    improperly instructed the jury that Flucas could be convicted
    if criminal sexual activity was a motivating purpose of the
    transportation of an individual, and that the district court was
    required to instruct the jury that criminal sexual activity must
    be the dominant purpose in order to establish the requisite
    intent.
    7
    Because Flucas filed his notice of appeal on February 15, 2019,
    “after the . . . announce[ment of] a . . . sentence” on February 12, 2019,
    but “before the entry of the judgment” on February 25, 2019, his appeal
    is “treated as filed on the date of and after the entry [of the judgment].”
    Fed. R. App. P. 4(b)(2).
    UNITED STATES V. FLUCAS                     15
    In interpreting the elements for transportation and travel
    offenses, we have consistently held that a dominant,
    significant, or motivating purpose to engage in criminal
    sexual activity satisfies the intent requirement. In United
    States v. Kinslow, 
    860 F.2d 963
     (9th Cir. 1988), disapproved
    of on other grounds by United States v. Brackeen, 
    969 F.2d 827
    , 829 (9th Cir. 1992) (en banc) (per curiam), we affirmed
    the defendant’s conviction for “interstate transportation of a
    minor for sexual purposes in violation of 
    18 U.S.C. § 2423
    .”
    
    Id. at 964, 970
    . In rejecting the defendant’s assertion that
    “the evidence was legally insufficient to support his
    conviction . . . because sexual misconduct was not a dominant
    purpose in the transportation of [the minor] across state
    lines,” we responded that “[i]n this circuit, a federal crime
    under 
    18 U.S.C. § 2423
     exists if the immoral activity is one
    of the dominant purposes of the transportation.” 
    Id. at 967
    (citation and internal quotation marks omitted). We further
    emphasized that it was “not necessary . . . that the immoral
    activity be the only purpose of the trip.” 
    Id.
     Instead, we
    concluded that:
    [The defendant] asserts that his only purpose
    in taking [the minor] across state lines was to
    insure his own safe passage from Arizona to
    California. While this may have been one of
    his goals, the jury was entitled to find that [the
    defendant] also intended to assert sexual
    control over the females in the . . . family and
    that this was one of the reasons he took them
    all into California. . . . A rational trier of fact
    could have found that one of the dominant
    16                     UNITED STATES V. FLUCAS
    purposes in transporting [the minor] across
    state lines was to have her available to him for
    immoral, sexual purposes.
    
    Id.
     at 967–98.
    In United States v. Lukashov, 
    694 F.3d 1107
    , 1110 (9th
    Cir. 2012), we considered the defendant’s challenge to his
    conviction for aggravated sexual abuse in violation of
    
    18 U.S.C. § 2241
    (c).8 The defendant maintained that the
    evidence supporting his conviction was insufficient because
    “his purpose in traveling to New York and back to Oregon
    was to pick up and deliver goods in his capacity as a
    long-haul truck driver.” 
    Id. at 1118
    . The district court
    instructed the jury that:
    The government need not prove that the
    Defendant traveled across a state line for the
    sole and exclusive purpose of engaging in a
    sexual act. A person may have different
    purposes or motives for travel and each may
    8
    
    18 U.S.C. § 2241
    (c) provides in pertinent part:
    Whoever crosses a State line with intent to engage in a
    sexual act with a person who has not attained the age of
    12 years, . . . knowingly engages in a sexual act with
    another person who has not attained the age of 12 years,
    or knowingly engages in a sexual act under the
    circumstances described in subsections (a) [by force or
    threat] and (b) [by other means in a federal enclave]
    with another person who has attained the age of 12
    years but has not attained the age of 16 years (and is at
    least 4 years younger than the person so engaging), or
    attempts to do so, shall be fined under this title and
    imprisoned for not less than 30 years or for life.
    UNITED STATES V. FLUCAS                    17
    prompt in varying degrees the act of making
    the journey. For purposes of this element, the
    government must prove beyond a reasonable
    doubt that a dominant, significant, or
    motivating purpose of Defendant’s travel
    across a state line was to engage in a sexual
    act with [the minor]. In other words, the
    government must prove the sexual act was not
    merely incidental to the travel.
    
    Id.
     (alteration omitted) (emphasis added). Unpersuaded by
    the defendant’s assertion that criminal sexual activity must be
    the sole purpose for his travels, we held that:
    A rational jury could have found beyond a
    reasonable doubt that once [the defendant]
    formed the intent to sexually abuse [the
    minor], whether that occurred before he
    started the trip or only after he dropped off
    [another minor] in Montana and was alone in
    his truck with [his victim], he had that illicit
    intent for the rest of the trip, until he returned
    her to her mother in Portland. Given the
    repeated instances of abuse after the first time
    in Montana, a jury could rationally infer that
    [the defendant] crossed the Montana–North
    Dakota and subsequent state lines with a
    dominant, significant, or motivating purpose
    of committing additional sexual acts. That
    [the defendant] also had a commercial
    purpose for crossing state lines does not
    negate the inference that he had a significant
    or motivating purpose to continue abusing
    [the minor] because, as the district court
    18               UNITED STATES V. FLUCAS
    correctly instructed the jury, the government
    did not have to prove that sexually abusing
    [the minor] was the sole purpose of [the
    defendant’s] interstate travel. . . .
    
    Id.
     at 1118–19 (citation and internal quotation marks omitted)
    (emphases added).
    In reaching this conclusion, we relied on the Tenth
    Circuit’s decision in United States v. Cryar, 
    232 F.3d 1318
    (10th Cir. 2000). See id. at 1119. In Cryar, the defendant
    asserted that there was insufficient evidence supporting his
    conviction for “cross[ing] the state line between Texas and
    Oklahoma with the intent to engage in a sexual act with a
    six-year old girl in violation of 
    18 U.S.C. § 2241
    (c).”
    
    232 F.3d at 1319
    . The defendant specifically argued that “the
    dominant purpose of his crossing the state line . . . was to
    earn a living, and not to commit a sexual act.” 
    Id. at 1324
    .
    The Tenth Circuit disagreed, concluding that “there was
    ample evidence for a jury to determine that a motivating or
    dominant purpose of [the defendant’s] travels to Oklahoma
    was to spend time with and attempt to engage in sexual acts
    with a child under twelve years old.” 
    Id.
     (citation omitted)
    (emphasis added).
    In United States v. Lindsay, 
    931 F.3d 852
    , 864 (9th Cir.
    2019), we applied Lukashov and rejected a challenge to a jury
    instruction delineating the intent requirements for a
    conviction under 
    18 U.S.C. § 2423
    . In that case, the district
    court instructed the jury that:
    the United States does not have to prove that
    Defendant traveled in foreign commerce for
    the sole and exclusive purpose of engaging in
    UNITED STATES V. FLUCAS                     19
    illicit sexual conduct. The government must
    prove that a dominant, significant, or
    motivating purpose of Defendant’s travel in
    foreign commerce was to engage in illicit
    sexual conduct.
    
    Id. at 858
     (internal quotation marks omitted) (emphasis
    added). In addressing the defendant’s assertion that the
    statutory term “‘for the purpose of’ clearly refers to a but-for
    causation standard, contrary to the ‘dominant, significant, or
    motivating’ standard the district court applied,” we clarified
    that:
    It is not obviously wrong to interpret “for the
    purpose of” as applying to any dominant,
    significant, or motivating purpose to account
    for that fact, as a plain understanding of the
    phrase can encompass multiple intentions.
    For instance, in common conversation a
    person can travel to the grocery store “for the
    purpose of” buying milk and getting gas if
    both milk and gas are motivating reasons for
    the excursion.
    
    Id. at 864
     (emphasis added). In light of consistent precedent
    that a motivating purpose to engage in illicit sexual activity
    may support the intent requirements for transportation and
    travel offenses, we held that “the district court did
    not plainly err by instructing the jury that [the defendant]
    traveled in foreign commerce for the purpose of engaging in
    illicit sexual activity if that purpose was dominant,
    significant, or motivating.” 
    Id.
     (emphasis added). Although
    we applied plain error review in rejecting the defendant’s
    20               UNITED STATES V. FLUCAS
    challenge to the jury instruction, we nonetheless adhered to
    the principles articulated in Lukashov that the defendant’s
    contention “ignore[d] the human ability and propensity to act
    in light of multiple motives and purposes.” 
    Id. at 864
    , quoting
    Lukashov, 694 F.3d at 1118.
    The dissent minimizes the import of Lindsay because it
    was decided on plain error review. See Dissenting Opinion,
    pp. 55–56. Although “[a]n error cannot be plain where there
    is no controlling authority on point and where the most
    closely analogous precedent leads to conflicting results,”
    United States v. Gnirke, 
    775 F.3d 1155
    , 1164 (9th Cir. 2015)
    (citation and internal quotation marks omitted), that was not
    the standard applied in Lindsay. Rather, we considered
    Lukashov and concluded that it was not error to instruct the
    jury regarding the defendant’s “motivating purpose.”
    931 F.3d at 864. Notably absent was any mention of the lack
    of “controlling authority” or conflicting precedent. Gnirke,
    775 F.3d at 1164. In any event, in order for plain error to
    exist, there must first be error. See United States v. Johnson,
    
    979 F.3d 632
    , 636 (9th Cir. 2020), as amended. In Lindsay,
    we found none. See Lindsay, 931 F.3d at 864.
    The dissent’s conclusion that there was no plain error in
    Lindsay “[g]iven the confusion in the courts,” rests upon a
    proposition which we never mentioned or relied on.
    Dissenting Opinion, pp. 55–56. Rather, our holding that the
    district court did not err in instructing the jury that a
    dominant, significant, or motivating purpose suffices to
    establish the requisite intent is bolstered by a long line of
    consistent and uniform cases from our sister circuits.
    In United States v. Hayward, 
    359 F.3d 631
     (3d Cir. 2004),
    the defendant asserted that “the District Court should have
    UNITED STATES V. FLUCAS                     21
    instructed the jury that criminal sexual activity had to be ‘the
    dominant’-rather than ‘a significant or motivating’-purpose
    of the trip to England in order to convict.” 
    Id. at 637
    (emphases in the original). Instead, the district court
    instructed the jury that:
    It is not necessary for the government to prove
    that the illegal sexual activity was the sole
    purpose for the transportation. A person may
    have several different purposes or motives for
    such travel, and each may prompt in varying
    degrees the act of making the journey. The
    government must prove beyond a reasonable
    doubt, however, that a significant or
    motivating purpose of the travel across state
    or foreign boundaries was to have the
    individual transported engage in illegal
    sexual activity. In other words, the illegal
    sexual activity must have not been merely
    incidental to the trip.
    
    Id.
     (emphasis in the original). In approving the district
    court’s instruction, the Third Circuit observed that:
    [The defendant] points to no case in which
    any Court of Appeals required a jury
    instruction that criminal sexual activity must
    be the dominant purpose of interstate travel to
    support a conviction under 
    18 U.S.C. § 2423
    (a). The Government relies on
    decisions by the First, Second, Fifth, Sixth,
    Seventh and Tenth Circuits, in which criminal
    sexual activity was one of a number of
    multiple motives for interstate travel. Those
    22               UNITED STATES V. FLUCAS
    courts declined to reverse convictions where
    the respective district court had refused or
    failed to give “the dominant purpose” jury
    instruction that [the defendant] now requests.
    
    Id. at 638
     (citations omitted) (emphasis in the original).
    In United States v. Campbell, 
    49 F.3d 1079
     (5th Cir.
    1995), the Fifth Circuit similarly analyzed the intent
    requirements for 
    18 U.S.C. § 2421
     and 
    18 U.S.C. § 2423
    . See
    
    id. at 1082
    . The defendant asserted that “the evidence was
    insufficient to allow a reasonable jury to find that his
    dominant purpose in traveling was to engage in prostitution.”
    
    Id.
     (internal quotation marks omitted). The defendant
    “question[ed] whether a dominant purpose can exist under the
    Mann Act when an equally compelling but innocent purpose
    for traveling exists,” and asserted that the prostitute’s “visit
    was motivated at least equally by the desire to visit her
    child.” 
    Id. at 1083
     (internal quotation marks omitted). The
    Fifth Circuit rejected “this line of arithmetic hairsplitting,”
    because “[t]he dominant requirement does not impose a but
    for limitation on the defendant’s intent.” 
    Id.
     (internal
    quotation marks omitted). The Fifth Circuit explained that:
    In determining whether a dominant purpose
    exists, we instead ask whether the illicit
    behavior is one of the efficient and
    compelling purposes of the travel.
    Accordingly, many purposes for traveling
    may exist, but, as long as one motivating
    purpose is to engage in prostitution, criminal
    liability may be imposed under the Act. When
    no dominant purpose exists, it is because any
    UNITED STATES V. FLUCAS                      23
    such purpose was either non-existent or
    incidental.
    
    Id.
     (citations and internal quotation marks omitted) (emphasis
    added). The Fifth Circuit concluded that “[w]hile it is true
    that [the prostitute] did have a child in the area, and they
    could have been traveling in order to visit the child, this fact
    is not inconsistent with the prostitution plan. A reasonable
    jury could find beyond a reasonable doubt that the group was
    traveling to New Mexico to visit [the prostitute’s] daughter
    and engage in prostitution.” 
    Id.
     (emphasis in the original);
    see also United States v. Hitt, 
    473 F.3d 146
    , 152 (5th Cir.
    2006) (holding that evidence that the defendants “engage[d]
    in a grooming process designed to reduce [the victim’s]
    resistance to sexual advances” was sufficient to demonstrate
    that the defendants “transported the victim to Louisiana with
    an efficient and compelling purpose to engage in illicit sexual
    activity”) (citations and internal quotation marks omitted).
    In United States v. Vang, 
    128 F.3d 1065
     (7th Cir. 1997),
    the Seventh Circuit, in affirming a conviction under
    
    18 U.S.C. § 2423
    (b), explained that the evolving intent
    standard for transportation and travel offenses originated with
    the Mann Act. The Seventh Circuit observed that “[t]hough
    enacted in 1994, the statutory antecedents of § 2423(b) date
    back to the early part of this century.” Id. at 1069. “Congress
    made the statute gender-neutral in a 1986 amendment, retired
    the purpose test for interstate transportation, and clarified the
    amorphous phrase any immoral purpose by narrowing the
    statute’s coverage to illegal sexual activity.” Id. (footnote
    reference and internal quotation marks omitted). “Section
    2423 evolved from this same legislative initiative as an effort
    to protect minors from predatory sexual conduct by adults,”
    and “[i]n 1994, Congress created § 2423(b) in a further
    24               UNITED STATES V. FLUCAS
    attempt to expand the protection of minors. The new statute
    punishes mere travel in interstate commerce—even if no
    transportation of a minor was involved—if the defendant is
    found to have traveled for the purpose of engaging in any
    sexual act (as defined in another Code section) with a minor.”
    Id.
    The Seventh Circuit concluded that the Supreme Court’s
    statement in Mortensen v. United States, 
    322 U.S. 369
     (1944)
    that, under the Mann Act, illicit sexual activity “must be the
    dominant motive of such interstate movement” was dicta. Id.
    at 1071 (emphasis in the original). The Seventh Circuit
    observed that “many circuits have upheld jury instructions
    and convictions where an immoral purpose was at least one
    of the purposes motivating the interstate transportation.” Id.
    (citations and internal quotation marks omitted) (emphasis
    added). “Other courts have used a dominant purpose
    standard, but have regarded dominant as synonymous with
    compelling or motivating, and they have never held—as
    Defendants urge here—that interstate travel can have only
    one dominant purpose.” Id. (citations and internal quotation
    marks omitted). In approving the jury instruction provided by
    the district court, the Seventh Circuit held that:
    the district court’s instructions to the jury
    interpreting § 2423(b)’s “purpose” element
    properly reflect this circuit’s law. At the most
    fundamental level, the defendants fail to
    convince us that Mortensen’s use of the word
    “dominant” grafted a new requirement onto
    the Mann Act that an immoral purpose must
    be “the dominant purpose” of interstate travel.
    Congress has not used the word “dominant” in
    either the Mann Act or § 2423(b), and we are
    UNITED STATES V. FLUCAS                    25
    not prepared to read such a requirement into
    the statutes. . . . Courts . . . have consistently
    used the word “dominant” to mean merely
    “significant” or “compelling” or “efficient”;
    there has never been any implied requirement
    of preeminence of purpose. We are simply not
    willing to break ranks with our sister circuits
    on this matter for the sake of semantic purity.
    Id. at 1072.
    In United States v. Perkins, 
    948 F.3d 936
     (8th Cir. 2020),
    the Eighth Circuit recently considered the intent requirements
    for 
    18 U.S.C. § 2423
    (a) in discerning the mens rea for
    violations of 
    18 U.S.C. § 2241
    (c). See 
    id. at 937
    . The Eighth
    Circuit explained that:
    The intent element of § 2241(c) is an issue of
    first impression for the Eighth Circuit. We
    have, however, addressed the intent element
    in cases involving the interstate transportation
    of a minor for the purpose of engaging in
    illegal sexual activity under 
    18 U.S.C. § 2423
    (a). To prove the intent element under
    § 2423(a), the illicit behavior must be one of
    the purposes motivating the interstate
    transportation, but need not be the dominant
    purpose, and the sexual activity just may not
    be merely incidental to the trip. The Eighth
    Circuit has also held intent for § 2423(a) may
    be inferred from all the circumstances,
    including the defendant’s own statements.
    26               UNITED STATES V. FLUCAS
    Id. at 938–39 (citations, alteration, and internal quotation
    marks omitted) (emphasis added).
    Thus, a common analytical thread runs through our
    precedent and that of other circuits for transportation
    offenses—the requisite intent may be established when the
    defendant has a dominant, significant, or motivating purpose
    for transporting an individual in order to engage in criminal
    sexual activity.
    The dissent basically advocates straying from this
    precedential harmony to hold that the district court committed
    instructional error as a matter of law. In its analytical
    journey, the dissent initially relies on Hansen v. Haff,
    
    291 U.S. 559
    , 562–63 (1934), a pre-World War II case, for
    the proposition that “[p]eople not of good moral character,
    like others, travel from place to place and change their
    residence. But to say that, because they indulge in illegal or
    immoral acts, they travel for that purpose, is to emphasize
    that which is incidental and ignore what is of primary
    significance.” Dissenting Opinion, p. 40. The dissent’s
    reliance on this general language from Hansen does nothing
    to diffuse the contemporary, consistent precedent underlying
    the district court’s proper instruction.
    The dissent next lands on Mortensen v. United States,
    
    322 U.S. 369
     (1944), Cleveland v. United States, 
    329 U.S. 14
    (1946), Hawkins v. United States, 
    358 U.S. 74
     (1958), and
    Daigle v. United States, 
    181 F.2d 311
     (1st Cir. 1950) in
    support of its contention that the defendant’s intent to illicit
    sex acts not be “a mere incident but rather an efficient
    purpose prompting and impelling the defendants to the
    transportation of the girls.” Dissenting Opinion, pp. 42–43,
    45–46. Our precedent and that of other circuits is consistent
    UNITED STATES V. FLUCAS                      27
    with this proposition, and also consistent with the instruction
    given by the district court that the criminal sexual activity
    could not be the “incidental purpose” of the defendant’s
    travel or transportation for criminal sexual activity as distinct
    from the travel. See Lukashov, 694 F.3d at 1118–19; Lindsay,
    931 F.3d at 864; Hayward, 
    359 F.3d at 637
    ; Campbell,
    
    49 F.3d 1083
    ; Perkins, 948 F.3d at 938–39.
    Importantly, in United States v. Ellis, 
    935 F.2d 385
     (1st
    Cir. 1991), the First Circuit took great pains to explain the
    consistency among the holdings in Daigle, Mortensen, and
    Hawkins, and the motivating purpose jury instruction:
    [The defendant] contends the court erred in
    rejecting his proffered alternative charge that
    the dominant purpose of the transportation
    must be the intent to engage in sexual activity
    with the minor. [The defendant] points to the
    Supreme Court’s holding in [Mortensen],
    construing an earlier Mann Act provision that
    preceded the present 
    18 U.S.C. § 2421
    . . . .
    Seven years after Mortensen, [in Daigle] this
    Circuit reviewed a district court’s instruction
    that the jury could convict so long as it found
    that one of the purposes of the interstate
    transportation was an immoral one.
    Notwithstanding Mortensen’s language on the
    dominant motive, we upheld the instruction.
    Both before 1950 and thereafter many other
    circuit courts took the same position, namely,
    that it was enough if one of the efficient
    purposes of the interstate transportation was
    to engage in the outlawed activity.
    28            UNITED STATES V. FLUCAS
    [The defendant] urges us to reconsider Daigle
    as being inconsistent with the Supreme
    Court’s venerable pronouncements in
    Mortensen and elsewhere on dominant
    motive. We are not persuaded. Quite apart
    from the 40 years that have elapsed since
    Daigle, and its widespread acceptance, we
    believe Daigle’s reasoning to be sound and
    not inconsistent with Mortensen. As the
    Daigle court pointed out, there was in
    Mortensen a total lack of evidence of any
    purpose for the interstate journey other than
    the innocent one of giving the women a
    deserved vacation from their work as
    prostitutes in their bawdy house. Thus the
    Court had no reason to consider the question
    of multiple purposes. It is true that the
    language in Mortensen alluding to a single
    dominant purpose was repeated in a footnote
    in [Hawkins], but in Hawkins the Court was
    concerned with a very different issue. No
    more than Mortensen itself does Hawkins
    contradict Daigle on the narrow issue of
    interstate journeys involving several motives.
    In the present case, as in Daigle, the district
    court . . . sufficiently met the requirements of
    Mortensen, as interpreted in Daigle, by
    requiring that criminal sexual activity be one
    of the several motives or purposes not a mere
    incident of the trip or trips, but instead was at
    least one of the defendant’s motivations for
    taking the trip in the first place.
    UNITED STATES V. FLUCAS                    29
    
    Id.
     at 389–90 (citations, alterations, footnote reference, and
    internal quotation marks omitted) (emphases in the original).
    The dissent also relies on a 1947 decision from the Eighth
    Circuit, Mellor v. United States, 
    160 F.2d 757
     (8th Cir. 1947).
    See Dissenting Opinion, p. 45 n.2. However, the Eighth
    Circuit has remained steadfast, as of 2020, in applying the
    motivating purpose standard. See Perkins, 948 F.3d
    at 938–39 (stating that “to prove the intent element under
    § 2423(a), the illicit behavior must be one of the purposes
    motivating the interstate transportation, but need not be the
    dominant purpose, and the sexual activity just may not be
    merely incidental to the trip”) (citations, alteration, and
    internal quotation marks omitted) (emphasis in the original).
    The dissent’s approach closely resembles the argument
    advanced by the defendant and rejected by the Third Circuit
    in Hayward. As the Third Circuit observed, “[the defendant]
    points to no case in which any Court of Appeals required a
    jury instruction that criminal sexual activity must be the
    dominant purpose of interstate travel to support a conviction
    under 
    18 U.S.C. § 2423
    (a).” 
    359 F.3d at 638
     (footnote
    reference omitted) (emphasis in the original). The Third
    Circuit further emphasized the uniformity of the circuits on
    this issue: the “First, Second, Fifth, Sixth, Seventh and Tenth
    Circuits, in which criminal sexual activity was one of a
    number of multiple motives for interstate travel . . . declined
    to reverse convictions where the respective district court had
    refused or failed to give the dominant purpose jury instruction
    that [the defendant] now requests.” 
    Id.
     (citations and internal
    quotation marks omitted) (emphasis in the original).
    Against this backdrop of uniform precedent, the dissent
    relies on United States v. Generes, 
    405 U.S. 93
     (1972), “a tax
    30               UNITED STATES V. FLUCAS
    case” for which the dissent contends “the particulars are not
    important to us.” Dissenting Opinion, p. 60. We disagree.
    The “particulars” are important because they reveal the lack
    of applicability of this tax case to the instruction given by the
    district court in this criminal case.
    In Generes, “[a] debt a closely held corporation owed to
    an indemnifying shareholder-employee became worthless in
    1962.” Generes, 
    405 U.S. at 94
    . The issue was “whether, for
    the shareholder-employee, that worthless obligation was a
    business or a nonbusiness bad debt” under the Internal
    Revenue Code and corresponding Treasury Regulations. 
    Id.
    The Treasury Regulation specified that “the character of the
    debt is to be determined by the relation which the loss
    resulting from the debt’s becoming worthless bears to the
    trade or business of the taxpayer. If that relation is a
    proximate one in the conduct of the trade or business in
    which the taxpayer is engaged at the time the debt becomes
    worthless, the debt comes within the exception provided by
    that subparagraph.” 
    Id.
     at 95 n.2 (alteration omitted)
    (emphasis added). The Supreme Court explained that “[i]n
    determining whether a bad debt is a business or a nonbusiness
    obligation, the Regulations focus on the relation the loss bears
    to the taxpayer’s business,” and that “[i]f, at the time of
    worthlessness, that relation is a proximate one, the debt
    qualifies as a business bad debt and the aforementioned
    desirable tax consequences then ensue.” 
    Id. at 95
     (internal
    quotation marks omitted). Resolution of the issue “turn[ed]
    on the proper measure of the required proximate relation.”
    
    Id.
    “At the trial Mr. Generes testified that his sole motive in
    signing the indemnity agreement was to protect his
    $12,000-a-year employment with the corporation,” and the
    UNITED STATES V. FLUCAS                          31
    district court instructed the jury that a “significant,” as
    opposed to a “dominant” motivation, “satisfie[d] the
    Regulations’ requirement of proximate relationship.” 
    Id. at 99
     (footnote reference omitted).
    The Supreme Court “conclude[d] that in determining
    whether a bad debt has a proximate relation to the taxpayer’s
    trade or business, as the Regulations specify, and thus
    qualifies as a business bad debt, the proper measure is that of
    dominant motivation, and that only significant motivation is
    not sufficient.” 
    Id. at 103
    . In delineating the dominant
    motivation standard for debts under the Tax Code and
    Treasury Regulations, the Supreme Court stated in full9 that:
    The dominant-motivation standard has the
    attribute of workability. It provides a
    guideline of certainty for the trier of fact. The
    trier then may compare the risk against the
    potential reward and give proper emphasis to
    the objective rather than to the subjective. As
    has just been noted, an employee-shareholder,
    in making or guaranteeing a loan to his
    corporation, usually acts with two
    motivations, the one to protect his investment
    and the other to protect his employment. By
    making the dominant motivation the measure,
    the logical tax consequence ensues and
    prevents the mere presence of a business
    motive, however small and however
    insignificant, from controlling the tax result at
    the taxpayer's convenience. This is of
    9
    The dissent omits the highlighted language utilized by the Supreme
    Court in articulating the standard. See Dissenting Opinion, p. 60.
    32               UNITED STATES V. FLUCAS
    particular importance in a tax system that is so
    largely dependent on voluntary compliance.
    
    Id. at 104
     (emphasis added).
    There are notable distinctions between the standard
    articulated in Generes and the standard applied to travel and
    transportation offenses for criminal sexual activity. First, the
    applicable Treasury Regulation, in defining nonbusiness debt,
    “focus[ed] on the relation the loss bears to the taxpayer’s
    business. If, at the time of worthlessness, that relation is a
    proximate one, the debt qualifies as a business bad debt and
    the aforementioned desirable tax consequences then ensue.”
    
    Id. at 96
    . In contrast, the criminal statutes prohibiting
    transportation of individuals and minors for criminal sexual
    activity are not premised on a “proximate relation,” instead
    establishing criminal liability for a defendant who “knowingly
    transports any individual in interstate or foreign commerce,
    or in any Territory or Possession of the United States, with
    intent that such individual engage in prostitution, or in any
    sexual activity for which any person can be charged with a
    criminal offense,” 
    18 U.S.C. § 2421
    (a) (emphases added), or
    who “knowingly transports an individual who has not attained
    the age of 18 years in interstate or foreign commerce, or in
    any commonwealth, territory or possession of the United
    States, with intent that the individual engage in prostitution,
    or in any sexual activity for which any person can be charged
    with a criminal offense.” 
    18 U.S.C. § 2423
    (a) (emphases
    added).
    Second, the Supreme Court developed the dominant
    motivation standard in the tax context in order to prevent “the
    mere presence of a business motive, however small and
    however insignificant, from controlling the tax result at the
    UNITED STATES V. FLUCAS                    33
    taxpayer’s convenience.” Generes, 
    405 U.S. at 104
    . This
    reasoning is consistent with the district court’s instruction
    that “the government must prove that the criminal sexual
    activity was not merely incidental to the transportation.”
    Third and finally, the Supreme Court emphasized that:
    The Code itself carefully distinguishes
    between business and non-business items. . . .
    The point . . . is that the tax statutes have
    made the distinction, that the Congress
    therefore intended it to be a meaningful one,
    and that the distinction is not to be obliterated
    or blunted by an interpretation that tends to
    equate the business bad debt with the
    nonbusiness bad debt.          We think that
    emphasis upon the significant rather than
    upon the dominant would have a tendency to
    do just that.
    
    Id.
     at 103–04 (emphases added). The dissent does not point
    to any similar distinctions intended by Congress in its efforts
    to prohibit the transportation of minors and other individuals
    for criminal sexual activity.
    Thus, the dissent ostensibly posits that the district court
    should have imported the “dominant motivation” standard
    used to determine a nonbusiness debt under the Treasury
    Regulations to instruct the jury concerning the charges
    brought against Flucas for transporting minors or other
    individuals and engaging in criminal sexual activity. See
    34                  UNITED STATES V. FLUCAS
    Dissenting Opinion, p. 60. In light of Lukashov,10 Lindsay,
    and consistent precedent from other circuits, we decline to
    hold that the district court erred as a matter of law in not
    instructing the jury based on the dissent’s formulation of a
    standard applied in tax cases.
    Contrary to the dissent’s assertions, see Dissenting
    Opinion, pp. 61–64, we are unconvinced that the non-
    retroactive amendment to 
    18 U.S.C. § 2423
    (b), a statute
    involving travel with intent to engage in illicit sexual conduct
    that Flucas was not charged under, has any bearing on the
    instructional issue raised in this appeal.11 Prior to December,
    2018, 
    18 U.S.C. § 2423
    (b) provided that:
    A person who travels in interstate commerce
    or travels into the United States, or a United
    States citizen or an alien admitted for
    permanent residence in the United States who
    travels in foreign commerce, for the purpose
    of engaging in any illicit sexual conduct with
    another person shall be fined under this title
    or imprisoned not more than 30 years, or both.
    
    18 U.S.C. § 2423
    (b)(2017) (emphasis added). In December,
    2018, pursuant to the Abolish Human Trafficking Act of
    2017, Congress amended 
    18 U.S.C. § 2423
    (b) in order to
    10
    The best argument that the dissent can muster against our reasoning
    in Lukashov is that it was dicta. See Dissenting Opinion, p. 56. But dicta
    or not, it was consistent with the other precedent approving the language
    in the district court’s instruction.
    11
    The amendment to 
    18 U.S.C. § 2423
    (b) to specify “a motivating
    purpose” standard has not been applied retroactively. See United States
    v. Lieu, 
    963 F.3d 122
    , 126 n.1 (D.C. Cir. 2020).
    UNITED STATES V. FLUCAS                    35
    “combat sex tourism” by removing “for the purpose of” from
    
    18 U.S.C. § 2423
    (b) and adding “with a motivating purpose”
    in its place. Pub. L. 115-392, December 21, 2018, 132 Stat
    5250, 5256.
    The Seventh Circuit’s discussion in United States v.
    McGuire, 
    627 F.3d 622
     (7th Cir. 2010) of the “purpose”
    requirement for 
    18 U.S.C. § 2423
    (b), prior to the 2018
    amendment, is instructive. In that case, the government only
    charged the defendant with violating 
    18 U.S.C. § 2423
    (b).
    The Seventh Circuit detailed the practical ramifications of the
    government’s charging decision resulting from the statutory
    distinctions:
    Section 2421 is the original Mann Act, as
    amended in minor respects. Section 2423(a),
    intended to protect minors from sexual
    predation, mirrors the Mann Act but imposes
    more severe penalties. Section 2423(b), the
    provision under which the defendant was
    prosecuted, was added to expand the
    protection of minors still further; it punishes
    travel in interstate commerce even if no minor
    is transported, if the purpose of the travel is
    sex with a minor. (Prosecutors frequently use
    this section to prosecute persons who cross
    state lines to rendezvous with minors whom
    they meet in online chat rooms). Section
    2423(c) was added to punish persons who
    travel in foreign commerce and have sex with
    a minor in the course of the trip regardless of
    what the defendant intended when he set out
    on it. It is apparent that if, as the jury found,
    the defendant had molested [the victim] on
    36               UNITED STATES V. FLUCAS
    their travels, he violated sections 2421,
    2423(a), and 2423(c). But inexplicably the
    government charged the defendant only with
    violating section 2423(b), which requires that
    the travel be for the purpose of engaging in
    illegal sexual activity. This charging decision
    . . . enabled the defendant to argue that the
    purpose of his trips was merely to conduct
    retreats; sex was not the purpose but a
    welcome byproduct . . . of the opportunities
    that the retreats created, as the boys were
    more vulnerable when far from home and the
    defendant’s molestation of them was less
    likely to be detected by his religious
    superiors, who as we know had suspected him
    for many years of being a child molester yet
    had taken no effective steps to protect young
    boys from him.
    
    Id. at 624
     (citations omitted) (emphasis in the original).
    In its amended form, 
    18 U.S.C. § 2423
    (b) requires that the
    government demonstrate that “a motivating purpose” of the
    defendant’s travels was to engage in illicit sexual activity.
    See 
    18 U.S.C. § 2423
    (b) (2021). It bears emphasizing that,
    despite decades of precedent holding that a dominant,
    significant, or motivating purpose may suffice to establish the
    requisite intent for 
    18 U.S.C. § 2423
    (a), Congress did not
    amend that statutory provision in any fashion. Notably,
    
    18 U.S.C. § 2423
    (a), in stark contrast with the amended
    version of 
    18 U.S.C. § 2423
    (b), does not use the term
    “purpose,” instead providing that “[a] person who knowingly
    transports an individual who has not attained the age of
    18 years in interstate or foreign commerce, or in any
    UNITED STATES V. FLUCAS                     37
    commonwealth, territory or possession of the United States,
    with intent that the individual engage in prostitution, or in
    any sexual activity for which any person can be charged with
    a criminal offense.” 
    18 U.S.C. § 2423
    (a) (emphasis added).
    “We do not construe statutory phrases in isolation; we read
    statutes as a whole, and where Congress includes particular
    language in one section of a statute but omits it in another, it
    is generally presumed that Congress acts intentionally and
    purposely in the disparate inclusion or exclusion.”
    Orozco-Lopez v. Garland, 
    11 F.4th 764
    , 776–77 (9th Cir.
    2021) (citations, alterations, and internal quotation marks
    omitted).
    In sum, we are not persuaded that the non-retroactive
    2018 amendment to § 2423(b) has any bearing on whether the
    district court abused its discretion in instructing the jury.
    Rather, we conclude that the district court correctly instructed
    the jury in accordance with our precedent and that of our
    sister circuits with respect to the intent requirements under
    
    18 U.S.C. §§ 2421
    (a) and 2423(a). After all, if Congress
    wanted to also amend § 2423(a), it could have easily done so.
    IV.    CONCLUSION
    The district court did not abuse its discretion in
    instructing the jury concerning the intent requirements for
    
    18 U.S.C. §§ 2421
    (a) and 2423(a). The instruction
    comported with our precedent, as well as that of our sister
    circuits, that the government must prove beyond a reasonable
    doubt that a dominant, significant, or motivating purpose of
    the transportation of the individuals was to engage in criminal
    sexual activity. The non-retroactive amendment of a statute
    that Flucas was not charged under does not undermine the
    38               UNITED STATES V. FLUCAS
    consistent precedent throughout the circuits rejecting the
    “dominant purpose” mens rea advocated by Flucas.
    AFFIRMED.
    SCHROEDER, Circuit Judge, concurring:
    This is not a complicated case. As Judge Rawlinson’s
    opinion documents, the language in this instruction has been
    provided to juries for decades and approved by appellate
    courts. It required the jury to find that illegal sexual activity
    was a “significant, dominant, or motivating purpose” of the
    travel. I concur in Judge Rawlinson’s opinion but write
    briefly only to underscore the key points that in my view
    undermine the dissent.
    First, the dissent views as binding language the Supreme
    Court used more than seventy years ago in a case that raised
    different issues than those raised here. The statute here
    requires interstate travel “with intent” to engage in unlawful
    sexual activity. See 
    18 U.S.C. §§ 2421
    (a), 2423(a). The
    Supreme Court’s opinion in Mortensen v. United States said
    that such intent must be a “dominant motive” for the travel.
    
    322 U.S. 369
    , 374 (1944). But the problem in Mortensen was
    that the defendants had no intent to engage in unlawful
    activities during their travel. See 
    id. at 372
    . They were
    taking a vacation from their business of running a brothel.
    See 
    id.
     That was “undisputed.” See 
    id.
     The Court was
    therefore not referring to any required quantum of unlawful
    intent. The dissent thus fastens on to words that do not come
    from a case where the defendant traveled with any unlawful
    intent, much less from a case like this, where the defendant
    UNITED STATES V. FLUCAS                     39
    intended to engage in unlawful sex with members of his
    household while moving them to a different state.
    Second, although the dissent acknowledges that the
    instruction the parties agreed to was appropriate, the only
    difference between that instruction and this one was the
    addition of the phrase “or motivating” to the adjectives
    “significant” and “dominant.” As the district court observed,
    it is hard to see how the addition makes any difference, and
    even harder to imagine how the jury would have understood
    “motivating” as describing a materially lower standard than
    “significant.” As the majority opinion demonstrates, courts
    have routinely treated the words as interchangeable. That this
    instruction has so long been given to juries without being
    questioned in this way only underscores the lack of
    perceptible difference between “dominant,” “significant,” and
    “motivating.”
    Third, the dissent surmises that this jury likely did see a
    difference because the first jury did not convict and the
    second jury did. Even assuming the phrase was added
    erroneously, we can not assume the addition could have been
    responsible for the different result. Retrials differ from first
    trials in many ways, only some of which might affect the
    jury’s perceptions. Here, for example, in the second trial, the
    government changed its presentation to concentrate on the
    defendant’s activities during one time period rather than two.
    The second jury thus heard a more focused presentation that
    could have affected its understanding of the case. In contrast,
    for the change in the wording of the instruction to have
    possibly mattered, there would have to be some likelihood
    that the jury shot a perceived gap between “significant” and
    “motivating,” a gap neither the district judge, nor any other
    judges reviewing similar instructions has ever thought
    40                UNITED STATES V. FLUCAS
    existed. The dissent is thus not supported by facts, semantics,
    or precedent.
    BYBEE, Circuit Judge, dissenting:
    Rodney Flucas is not a sympathetic defendant. There is
    overwhelming evidence that Flucas groomed young girls for
    sex, including his own daughters. He has fathered at least ten
    children with these young women, making him the father of
    his own grandchildren. Although he likely can be charged for
    these acts in the states of Georgia, Oregon, and California, the
    question in this case is whether Flucas has violated a federal
    law, the Mann Act, 
    18 U.S.C. §§ 2421
    –24, for transporting
    women and minors across state lines with the intent to engage
    in criminal sexual activity. Flucas moved his family from
    Oregon to California when he accepted a new, better-paying
    position as a special education teacher in Stockton. But as the
    Court trenchantly observed: “People not of good moral
    character, like others, travel from place to place and change
    their residence. But to say that, because they indulge in
    illegal or immoral acts, they travel for that purpose, is to
    emphasize that which is incidental and ignore what is of
    primary significance.” Hansen v. Haff, 
    291 U.S. 559
    , 562–63
    (1934).
    At Flucas’s first trial, the district court instructed the jury
    that Flucas could be convicted only if the jury found that
    “criminal sexual activity was one of the dominant purposes,
    not merely an incidental purpose, for the transportation from
    one state to another.” That jury hung and was dismissed. At
    the second trial, the government requested a different
    instruction, over Flucas’s objections. The district court
    UNITED STATES V. FLUCAS                   41
    agreed to the instruction and told the jury it could convict
    Flucas if “sexual activity was a significant, dominant, or
    motivating purpose” for transporting the women across state
    lines. The second time the jury convicted Flucas.
    The question before us is a linguistic one. No court has
    considered whether “a motivating purpose” is different from
    “a dominant or significant purpose.” In my view, those terms
    are not synonymous.          The instruction lowered the
    government’s burden of proof, contrary to the Supreme
    Court’s decision in Mortensen v. United States, 
    322 U.S. 309
    (1944), and our own Mann Act decisions; and the error in
    instruction is not harmless beyond a reasonable doubt. Flucas
    may be guilty of committing heinous acts in multiple
    jurisdictions. But the government must show that his
    dominant or significant purpose for traveling between those
    jurisdictions was to commit those unlawful sexual acts. He
    may or may not have done so. I respectfully dissent.
    I
    In 1910, born out of a hysteria that “white slavers” were
    preying upon young women—coercing them into prostitution
    through threats, intimidation, and force—Congress passed
    what is commonly called the Mann Act. See United States v.
    Vang, 
    128 F.3d 1065
    , 1069–70 (7th Cir. 1997); David J.
    Langum, Crossing Over the Line: Legislating Morality and
    the Mann Act 3–4 (2006). Section 2 of the Act stated
    [A]ny person who shall knowingly transport
    or cause to be transported, or aid or assist in
    obtaining transportation for, or in
    transporting, in interstate or foreign
    commerce, or in any Territory or in the
    42               UNITED STATES V. FLUCAS
    District of Columbia, any woman or girl for
    the purpose of prostitution or debauchery, or
    for any other immoral purpose, or with the
    intent and purpose to induce, entice, or
    compel such woman or girl to become a
    prostitute or to give herself up to debauchery,
    or to engage in any other immoral practice . . .
    shall be deemed guilty of a felony . . . .
    White-Slave Traffic Act (Mann Act), Pub. L. No. 277, § 2, 
    36 Stat. 825
     (1910) (emphasis added), current version at
    
    18 U.S.C. § 2421
    . Alas, § 2 of the Mann Act used the term
    “intent.” Intent is an important, perfectly good legal concept,
    but sometimes in a statute, it is not particularly helpful. This
    is one of those instances. The question is, what kind of intent
    counts? The Mann Act isn’t clear on this point.
    The Supreme Court took up the question in Mortensen v.
    United States, 
    322 U.S. 369
     (1944). The Mortensens were
    husband and wife who lived in Nebraska, where they ran a
    house of prostitution. In 1940, they traveled by car to Salt
    Lake City to visit family and national parks. They invited
    two of the prostitutes they managed to accompany them on
    the trip, and the girls accepted. No acts of prostitution
    occurred along the route, nor while they were in Utah. When
    the Mortensens and the two young women returned to
    Nebraska, the girls resumed their sex trade. The United
    States charged the Mortensens with violating the Mann Act
    by transporting the girls in interstate commerce from Salt
    Lake City to Nebraska for the purpose of engaging in
    prostitution. The Court wrote that “[a]n intention that the
    women or girls shall engage in the conduct outlawed by
    Section 2 must be found to exist before the conclusion of the
    interstate journey and must be the dominant motive of such
    UNITED STATES V. FLUCAS                            43
    interstate movement.” 
    Id. at 374
     (emphasis added). On that
    basis, the Court overturned the conviction. Even “assum[ing]
    that [the Mortensens] anticipated that the two girls would
    resume their activities as prostitutes,” the “interstate vacation
    trip . . . was [not] undertaken . . . for the purpose of, or as a
    means of effecting or facilitating, such activities.” 
    Id.
     at
    374–75. According to the Court, “[w]hat Congress has
    outlawed by the Mann Act, . . . is the use of interstate
    commerce as a calculated means for effectuating sexual
    immorality.” 
    Id. at 375
     (emphasis added). The Court
    repeated its “dominant purpose” formulation in subsequent
    Mann Act cases. See, e.g., Hawkins v. United States,
    
    358 U.S. 74
    , 79 (1958) (“dominant purpose”); Cleveland v.
    United States, 
    329 U.S. 14
    , 20 (1946) (“dominant motive”).
    The statute has been amended several times since
    Mortensen. See Vang, 
    128 F.3d at 1069
     (recounting the
    history). The version Flucas was convicted under reads,
    “[w]hoever knowingly transports any individual in interstate
    or foreign commerce . . . with intent that such individual
    engage in prostitution, or in any sexual activity for which any
    person can be charged with a criminal offense, or attempts to
    do so, shall be fined under this title or imprisoned not more
    than 10 years, or both.” 
    18 U.S.C. § 2421
    (a).1 Despite
    amendments that changed the Mann Act’s “intent and
    purpose” language to “intent,” Mortensen continues to
    influence our thinking in this area. But the Supreme Court’s
    language in Mortensen has also caused great confusion.
    1
    Flucas was also convicted of violating 
    18 U.S.C. § 2423
    (a). The
    language of § 2423(a) is substantially similar to § 2321(a), but applies to
    transportation of minors.
    44                UNITED STATES V. FLUCAS
    A
    Federal courts since Mortensen have struggled with the
    Court’s “dominant motive” formulation. Indeed, “courts turn
    handsprings trying to define ‘dominant.’” United States v.
    McGuire, 
    627 F.3d 622
    , 625 (7th Cir. 2010). For some time,
    the courts debated whether Mortensen meant that the jury
    must find that illicit sexual conduct was “the dominant
    motive” or “a dominant motive” for the interstate
    transportation. We were concerned that a person could have
    more than one dominant purpose. The courts quickly agreed,
    however, that people travel with mixed motives, and that so
    long as “a dominant motive” was to traffic in prostitution or
    another illegal criminal sex offense, the Mann Act was
    satisfied. See, e.g., United States v. Drury, 
    582 F.2d 1181
    ,
    1185 (8th Cir. 1978) (prostitution must be “one of the
    dominant purposes of such interstate travel”); United States
    v. Snow, 
    507 F.2d 22
    , 24 (7th Cir. 1974) (“It now appears
    settled that prostitution or other immoral conduct, need not be
    the sole reason for the transportation . . . .”); United States v.
    Salter, 
    346 F.2d 509
    , 511 (6th Cir. 1965) (“It is sufficient if
    prostitution was only one of the dominant purposes.”);
    Dingess v. United States, 
    315 F.2d 238
    , 240 (4th Cir. 1963)
    (“If [the defendant] had some other lawful, but subordinate,
    purpose which he also sought to serve, the existence of that
    lawful purpose cannot purify or legitimize the dominant
    purpose of prostituting his female companions.”); Dunn v.
    United States, 
    190 F.2d 496
    , 497 (10th Cir. 1951) (“It is
    enough that one of the dominant purposes was prostitution or
    debauchery.”). See also Forrest v. United States, 
    363 F.2d 348
    , 350 (5th Cir. 1966).
    But the courts thought that the phrase “dominant motive”
    was still confusing and began tinkering with alternative word
    UNITED STATES V. FLUCAS                                45
    formulas. Word formulas in statutes are typically Congress’s
    effort to capture a “mood.” Universal Camera Corp. v.
    NLRB, 
    340 U.S. 474
    , 487 (1951). Moods can be hard to
    describe—a mood is itself “not . . . a body of rigid rules.” 
    Id.
    Nevertheless, “[a]s legislation that mood must be respected,
    even if it can only serve as a standard for judgment.” 
    Id.
     In
    the case of the Mann Act, the federal courts tried to capture
    Congress’s mood by adding their own word formulas. As I
    demonstrate below, as we changed word formulas, we strayed
    from Mortensen’s determination that the Mann act requires
    engaging in illicit sexual activity play a dominant role in the
    decision to travel between jurisdictions.
    In the aftermath of Mortensen, a number courts of appeals
    looked to causation language borrowed from tort. They
    variously required the government to prove that sex
    trafficking was an “efficient purpose,” an “efficient and
    compelling purpose,” or a “compelling and efficient
    purpose.”2 See, e.g., Daigle v. United States, 
    181 F.2d 311
    ,
    2
    The earliest use of “efficient purpose” in a published opinion
    appears just two years after Mortensen. See United States v. Mellor, 
    71 F. Supp. 53
    , 62 (D. Neb. 1946), aff’d, 
    160 F.2d 757
     (8th Cir. 1947). The
    district court in its explanation of the instruction referred to “efficient
    purpose” as “explanatory causation.” 71 F. Supp. at 62. The related term
    “efficient cause” has its origins in tort. See Jeremiah Smith, Legal Cause
    in Actions of Tort, 
    25 Harv. L. Rev. 303
     (1912). Professor Smith’s focus
    was whether “the defendant’s tort [was] a substantial factor in producing
    the damage complained of.” 
    Id. at 310
    . He suggested that possible word
    substitutes for “substantial” might include “efficient,” “continuously
    efficient,” and “active and efficient” factor. 
    Id.
     at 310 n.22. Anticipating
    some of the developments here, he also suggested that “a substantial
    factor” meant “[n]ot the sole factor, nor the predominant factor. Enough
    if it is a substantial part of the causative antecedents; if it is one of several
    substantial factors.” 
    Id. at 311
    . See also Scott G. Johnson, The Efficient
    Proximate Cause Doctrine In California: Ten Years After Garvey, 2 J. Ins.
    46                 UNITED STATES V. FLUCAS
    314 (1st Cir. 1950) (requiring the government to “prove that
    the defendants’ immoral purpose was ‘not a mere incident but
    rather an efficient purpose prompting and impelling the
    defendants to the transportation of the girls.’” (quoting Mellor
    v. United States, 
    160 F.2d 757
    , 764 (8th Cir. 1942)); Reamer
    v. United States, 
    318 F.2d 43
    , 49 (8th Cir. 1963); United
    States v. Campbell, 
    49 F.3d 1079
    , 1082 (5th Cir. 1995) (“It is
    enough that one of the dominant purposes was prostitution or
    debauchery. It suffices if one of the efficient and compelling
    purposes in the mind of the accused in the particular
    transportation was illicit conduct of that kind.” (emphasis
    added) (quoting Forrest, 
    363 F.2d at 349
    ); United States v.
    Tyler, 
    424 F.2d 510
    , 512 (10th Cir. 1970) (“‘It is enough that
    one of the purposes was prostitution. It suffices that one of
    the efficient and compelling purposes in the mind of the
    accused in a particular transportation was the prostitution
    charged in the indictment.’”); United States v. Schneider,
    
    801 F.3d 186
    , 194 (3d Cir. 2015) (“It now appears settled that
    . . . immoral conduct, need not be the sole reason for the
    transportation; the Act may be violated if [immoral conduct]
    is a dominant or a compelling and efficient purpose.”
    (alteration in original) (quoting United States v. Snow,
    507 F.2 22, 24 (7th Cir. 1974)). In 1997, in an influential
    opinion reviewing the Mann Act’s history and the cases, the
    Seventh Circuit observed that “courts have used a “dominant
    purpose’ standard but have regarded ‘dominant’ as
    synonymous with ‘compelling’ or ‘motivating.’” Vang,
    
    128 F.3d at 1071
    . The court concluded that “[c]ourts . . .
    have consistently used the word ‘dominant’ to mean merely
    ‘significant’ or ‘compelling’ or ‘efficient.’” Inexplicably, it
    further opined that “there has never been any implied
    Coverage 1, 5–6 (1999) (noting that in tort “efficient proximate cause”
    means “predominating cause”).
    UNITED STATES V. FLUCAS                     47
    requirement of preeminence of purpose.” 
    Id. at 1072
    . See
    also McGuire, 
    627 F.3d at 625
    .
    Although, prior to Vang, the phrase “motivating purpose”
    had not appeared regularly in cases, it had been used by some
    courts, usually in a casual way. See Campbell, 
    49 F.3d at 1083
    . Around 2000, however, the phrase began to show up
    more frequently. In United States v. Cryar, for example, the
    district court had instructed the jury that the illegal sexual
    conduct need not be the sole purpose for the travel, but was
    sufficient under the Mann Act if it was “one of the
    Defendant’s efficient and compelling purposes, or one of the
    Defendant’s dominant purposes.” 
    232 F.3d 1318
    , 1324 (10th
    Cir. 2000). The court of appeals affirmed the conviction and,
    in the process, subtly altered the word formula. The court
    commented that “there was ample evidence for a jury to
    determine that a motivating or dominant purpose” for Cryar’s
    travel was to engage in sexual conduct with a minor. 
    Id.
    (emphasis added). The language of “motivating purpose”
    was the Tenth Circuit’s imprecise gloss on what the district
    court had instructed.
    The Third Circuit followed suit, approving the addition of
    “a motivating purpose” to jury instructions. In United States
    v. Hayward, Hayward and his wife owned a competitive
    cheerleading school and chaperoned six teenaged girls on a
    trip to London. 
    359 F.3d 631
     (3d Cir. 2004). While there,
    Hayward plied them with alcohol and engaged in sexual
    activity with them. At trial, Hayward argued that the jury
    must find the illegal sexual conduct was “a dominant
    purpose” for the trip. The district court declined and
    instructed the jury that it was sufficient if the conduct was “a
    significant or motivating purpose” of the trip to London. 
    Id. at 638
     (emphasis added). On appeal, Hayward altered his
    48               UNITED STATES V. FLUCAS
    strategy and claimed that the only proper instruction was that
    the trip had to be “the dominant purpose” for the trip. The
    court rejected all of Hayward’s formulations, finding that the
    jury instruction was proper. 
    Id.
    Hayward’s emendation was picked up in a prominent
    federal jury instruction treatise. In a section discussing the
    Mann Act and citing Hayward as its authority, Modern
    Federal Jury Instructions recommends the following
    instruction for the intent element of 
    18 U.S.C. § 2421
    :
    In order to establish this element, it is not
    necessary for the government to prove that
    engaging in prostitution was the sole purpose
    for crossing the state line. A person may have
    several different purposes or motives for such
    travel, and each may prompt in varying
    degrees the act of making the journey. The
    government must prove beyond a reasonable
    doubt, however, that a significant or
    motivating purpose of the travel across a state
    line was that [said individual(s)] would
    engage in prostitution. In other words, that
    illegal activity must not have been merely
    incidental to the trip.
    3 Leonard B. Sand, et al., Modern Federal Jury Instructions:
    Criminal, ¶ 64.01, Instr. 64-4 (2021) (brackets in original).
    The treatise blended two distinct concepts. The second
    sentence quoted above uses “purposes” and “motives” as
    nouns and treats them as synonyms. But the third sentence
    converts “motive” to an adjective modifying “purpose.” As
    a matter of syntax, the treatise can’t have it both ways.
    Having suggested that “purposes” and “motives” are the
    UNITED STATES V. FLUCAS                            49
    same, a “motivating purpose” is redundant. It’s like saying
    “purposeful purpose” or “motivating motive.”
    Confusion followed in the commentary. Modern Federal
    Jury Instructions proposes that the illicit sexual activity does
    not have to be “the dominant motive, but only that it be a
    dominant motive in that it was a compelling or significant
    motivation for the travel.” 
    Id. ¶ 64
    .01, Instr. 64-4, Comment
    (emphasis added). That statement would accurately capture
    the pre-2000 consensus. The problem is that between the
    model instruction and the commentary, the treatise uses
    “significant purpose,” “motivating purpose,” “compelling
    motivation,” and “significant motivation” as equivalents. The
    inconsistency is not explained.3 Modern Federal Jury
    Instructions has found its way into district court instructions
    and been approved by at least one court of appeals. United
    States v. An Soon Kim, 471 F. App’x. 82, 84 (2d Cir. 2012)
    (quoting the district court’s instructions, which quote from
    Modern Federal Jury Instructions, and citing the treatise with
    approval).
    3
    Compounding its own confusion, in the same paragraph, the treatise
    also favors eliminating use of the word “dominant” and the phrase
    “efficient and compelling purpose” in instructions because they are
    “likely to confuse the jury.” But, the treatise proposes using “the clearer
    terms ‘sole purpose’ and ‘significant or motivating purpose,’ which are
    easier to understand.” Modern Federal Jury Instructions: Criminal,
    ¶ 64.01, Instr. 64-4, Comment. Thus, in the same paragraph, the treatise
    proposes that courts may use “significant motivation,” “motivating
    purpose,” or “significant purpose” interchangeably, without any
    explanation of how those phrases are equivalent.
    50                   UNITED STATES V. FLUCAS
    B
    Our own precedent on the proper jury instruction in a
    Mann Act case has followed a similar twisted path. We first
    grappled with Mortensen’s “dominant motive” in Langford
    v. United States, 
    178 F.2d 48
     (9th Cir. 1949).4 Langford had
    acted as Jones’s pimp. Eventually Langford asked Jones to
    marry him, although he told her she would have to continue
    to engage in prostitution. Jones and Langford traveled to
    Tijuana to be married, after which they returned to Los
    Angeles where Jones resumed her prostitution. Citing
    Mortensen, we held that there was sufficient evidence that
    “[Langford’s] dominant motive” for the marriage was to get
    control of Jones and re-establish a relationship of pander and
    prostitute. . . and that the trip, marriage and all, had that
    primary end in view.” 
    Id. at 52
    . See also Powell v. United
    States, 
    347 F.2d 156
    , 157 (9th Cir. 1965) (“The trial court
    properly instructed the jury that the immoral purpose . . .
    [must] exist before the journey ends and supply the dominant
    motive for the trip.”).
    We soon began considering the problem of mixed
    motives. In Twitchell v. United States, we reconsidered our
    4
    We ignored Mortensen in Womble v. United States, 
    146 F.2d 263
    (9th Cir. 1945). Dewey Womble drove from Louisville, Kentucky, to
    Stockton, California with Stephen Culp and Dewel Kathleen Womble.
    After arriving, Dewel Kathleen Womble began working as a prostitute.
    Dewey Womble claimed “there was no evidence in that transporting
    Dewel Kathleen Womble he had any intent that she should practice
    prostitution.” 
    Id. at 263
    . We held that intent could be “infer[red] . . . from
    all the circumstances of the evidence.” 
    Id.
     The Supreme Court reversed
    our decision in a two-sentence opinion holding that there was “want of
    substantial evidence to sustain the conviction.” Womble v. United States,
    
    324 U.S. 830
    , 830 (1945) (per curiam).
    UNITED STATES V. FLUCAS                  51
    prior judgment affirming the conviction of one Harrison
    Rogers. 
    330 F.2d 759
     (9th Cir. 1964), on remand from, sub
    nom., Rogers v. United States, 
    376 U.S. 188
     (1964), vacating
    in part Twitchell v. United States, 
    313 F.3d 425
     (9th Cir.
    1963). Rogers ran a motel in Everett, Washington, in which
    several units were used for prostitution. A woman named
    Ryan worked at the motel and occasionally oversaw the
    prostitutes. When Ryan went to Portland, where she went on
    a drinking spree, Rogers went and picked her up and returned
    her to Everett, where she took several weeks to sober up
    before returning to work at the motel. We reversed Rogers’s
    conviction under the Mann Act:
    [T]here is no showing that Ryan’s trip to
    Portland was for an immoral purpose. It was
    to visit her home. The most that can be said
    of the return trip is that the dominant purpose
    was to get her sobered up and away from
    home, where she had her drinking problem.
    Nothing in the record would support a finding
    that either the or a dominant purpose of that
    trip was to have her resume immoral
    activities.
    
    Id. at 761
    .
    In Bush v. United States, we found the “sole issue” was
    “the intent of defendant—did he have the intent, purpose and
    motive in bringing the complaining witness to California to
    have her engage in immoral practices?” 
    267 F.2d 483
    , 485
    (9th Cir. 1959). In Bush’s case, the issue was not a
    particularly difficult one. Bush was convicted of taking a
    seventeen year old from Texas to California, where she began
    engaging in prostitution, jointly with Bush’s wife, who had
    52               UNITED STATES V. FLUCAS
    been a prostitute in Texas. Upholding the conviction, we
    stated that “[i]t was not necessary that such intent be the sole
    and single purpose of the transportation, if such purpose and
    intent was one of the reasons for the transportation.” 
    Id.
    (citation omitted).
    We followed Bush in United States v. Fox, when we made
    clear that it was “only necessary that the government prove
    that [prostitution, debauchery, or other immoral purpose] was
    one of the dominant purposes.” 
    425 F.2d 996
    , 999 (9th Cir.
    1970) (emphasis added). We approved the instruction as “a
    common and correct statement of the law.” 
    Id.
     We found no
    merits in the defendant’s claim that the “jury might have
    misinterpreted the instruction to include situations in which
    illicit activity was merely incidental to the purpose of the
    interstate journey.” 
    Id. at 1000
    . In a number of cases
    following Fox, we hewed closely to the line that the
    government must prove that unlawful sexual conduct was at
    least a dominant purpose for the travel. See United States v.
    Kinslow, 
    860 F.2d 963
    , 967 (9th Cir. 1988) (“In this circuit,
    a federal crime under 
    18 U.S.C. § 2423
     exists if the immoral
    activity is ‘one of the dominant purposes’ of the
    transportation. It is not necessary, therefore, that the immoral
    activity be the only purpose of the trip.” (quoting Fox,
    
    425 F.2d at 999
    )); United States v. Szymanski, 
    431 F.2d 946
    ,
    946 (9th Cir. 1970) (“a dominant motive”); Chargois v.
    United States, 
    267 F.2d 410
    , 412 (9th Cir. 1959) (“a second
    dominant and substantial purpose”). See also United States
    v. Rashkovski, 
    301 F.3d 1133
    , 1137 (9th Cir. 2002); United
    States v. Sangetti, 
    446 F.2d 552
    , 552 (9th Cir. 1971) (per
    curiam). Cf. Hett v. United States, 
    353 F.2d 761
    , 763 (9th
    Cir. 1965).
    UNITED STATES V. FLUCAS                            53
    In United States v. Lukashov, for the first time, we
    implicitly approved an instruction that a jury can convict on
    proof that the interstate travel was “a dominant, significant,
    or motivating purpose.” 
    694 F.3d 1107
    , 1118 (9th Cir. 2012)
    (emphasis added). Lukashov was a long-distance hauler and,
    on the suggestion of his wife, took his eight-year old
    stepdaughter with him across the country, sexually abusing
    her along the way. On appeal, Lukashov did not challenge
    the jury instructions.5 Instead, he argued that the evidence
    was insufficient to convict him under 
    18 U.S.C. § 2241
    (c)
    because the purpose of the trip was to deliver goods to the
    East Coast and return to Oregon. 
    Id.
     at 1118–19. We pointed
    out that Lukashov’s claim “ignores the human ability and
    propensity to act in light of multiple motives and purposes.”
    
    Id. at 1118
    . We found the evidence sufficient that “a jury
    5
    Before the district court, Lukashov requested an instruction that the
    government must prove beyond a reasonable doubt that “one of the
    dominant purposes of defendant’s interstate travel . . . was to engage in a
    sexual act [with his stepdaughter].” Proposed Jury Instructions by
    Alexander Lukashov, Jr, United States v. Lukashov, No. 3:14-cv-00502-
    BR (D. Or. filed June 21, 2010), ECF No. 87. Instead, the district court
    instructed the jury as follows:
    A person may have different purposes or motives for
    travel and each may prompt in varying degrees the act
    of making the journey. For purposes of the First
    Element,, the government must prove beyond a
    reasonable doubt that a dominant, significant, or
    motivating purpose of Defendants across a state line
    was to engage in a sexual act with [his stepdaughter].
    Final Jury Instructions as to Alexander Lukashov, Jr, United States v.
    Lukashov, No. 3:14-cv-00502-BR (D. Or. filed July 27, 2010), ECF
    No. 139. That jury instruction is, nearly word-for-word, the instruction
    approved by the Third Circuit in Hayward and adopted in Modern Federal
    Jury Instructions.
    54                UNITED STATES V. FLUCAS
    could rationally infer that Lukashov crossed the
    Montana–North Dakota and subsequent state lines with ‘a
    dominant, significant, or motivating purpose’ of committing
    additional sexual acts.” 
    Id. at 1119
     (quoting the district court
    instruction). See also 
    id.
     (“That Lukashov also had a
    commercial purpose for crossing state lines does not negate
    the inference that he had a significant or motiving purpose to
    continue abusing [his stepdaughter] . . . .”). In passing, we
    remarked that the district court “correctly instructed the jury,”
    but we did not recognize the gloss the district court had added
    to our prior cases by including the phrase “motivating
    purpose.” 
    Id. at 1119
    .
    Our subtle change in Lukashov reappeared in United
    States v. Lindsay, 
    931 F.3d 852
     (9th Cir. 2019). Lindsay was
    convicted under 
    18 U.S.C. § 2423
    (b) of traveling to the
    Philippines, where he had sex with a thirteen-year old girl and
    paid her family money. The district court in his case gave the
    jury effectively the same instruction found in Modern Federal
    Jury Instructions and that we nominally approved in
    Lukashov: “The government must prove that a dominant,
    significant, or motivating purpose of [Lindsay’s] travel in
    foreign commerce was to engage in illicit sexual conduct.”
    
    Id. at 858
    . Lindsay objected to the jury instruction on appeal,
    arguing that the statute required “but-for causation.” Because
    Lindsay failed to object in the trial court, we reviewed for
    plain error.
    “Plain error is error that is ‘clear’ or ‘obvious.’ 
    Id. at 864
    (emphasis added) (quoting Johnson v. United States 
    520 U.S. 461
    , 467 (1997)). Put another way, “plain error, as we
    understand that term, is error that is so clear-cut, so obvious,
    a competent district judge should be able to avoid it without
    benefit of objection.” United States v. Turman, 122 F.3d
    UNITED STATES V. FLUCAS                          55
    1167 (9th Cir. 1997), see United States v. Frady, 
    456 U.S. 152
    , 163 (1982) (error is plain only if trial judge is “derelict
    in countenancing it”). Thus, a court may determine that there
    was no error or that there was error, but it was not clear or
    obvious under current law.6 See, e.g., United States v.
    Ferreyro, No. 19-50325, 
    2021 WL 5414854
    , at *1 (9th Cir.
    2021) (“But, even assuming error, Ferreyro cites no authority
    to support that such error was obvious.”); United States v.
    Meza-Casillas, 15 F. App’x 408, 409 (9th Cir. 2001)
    (“Assuming without deciding that either or both arguments
    would have been well taken, the error, if any, was not ‘plain.’
    A ‘plain’ error means an error that ‘is so clear-cut, so obvious
    a competent district court judge should be able to avoid it
    without benefit of [any] objection.’ The error here, if any,
    does not meet that standard.). Contrary to the majority’s
    characterization of Lindsay, we did not hold that the
    instruction was not erroneous. See Maj. Op. at 20. Rather,
    citing Lukashov, we held that it was “not obviously wrong”
    and “the district court did not plainly err by instructing the
    jury that Lindsay traveled in foreign commerce for the
    purpose of engaging in illicit sexual activity if that purpose
    was dominant, significant, or motivating.” 
    Id. at 19
    (emphasis added). Put simply, the district court’s instruction
    in Lindsay may have been erroneous, but not clearly or
    obviously so.
    We are not on plain error review here. If we were, I
    would not only be compelled to follow Lindsay, but I would
    willingly follow it. Given the confusion throughout the
    federal courts, the district court’s instruction here was not
    6
    A court may also determine that an error was obvious but did not
    affect substantial rights or prejudice the defendant.
    56                   UNITED STATES V. FLUCAS
    obviously erroneous.7 But Flucas objected repeatedly to the
    instruction and made clear that he believed that the district
    court had reduced the government’s burden. Given the
    government’s change in requested instruction after the first
    jury hung, Flucas had every reason to object.
    Our decisions, like those of our sister circuits, are
    inconsistent. Our decision in Fox stated one standard—a
    standard we followed in many other cases. Lukashov and
    Lindsay indirectly approved a different instruction, without
    acknowledging the change in the instruction. Although those
    cases are more recent, neither compels our hand in this case.
    Lukashov was a sufficiency-of-the-evidence case in which the
    defendant apparently conceded the correctness of the
    instruction. Although we pronounced the instruction correct
    in passing, we did not consider the point raised by Flucas
    here. So our discussion of the correctness is dicta, at best.
    Lindsay was on plain error review.
    The troubling history of the jury instructions in Mann Act
    cases should give us pause and force us to ask: Is there a
    difference between “a dominant purpose,” “a significant
    purpose,” and “a motivating purpose”? If there is not, then
    why have we experimented with so many formulations? I
    take up these questions in the next section.
    7
    The majority takes this long-running confusion as a sign of the
    correctness of the instruction. Maj. Op. at 20 (“our holding . . . is
    bolstered by a long line of consistent and uniform cases from our sister
    circuits.”); see also 
    id.
     at 33–34 & n.10. That is, the instruction is correct
    because it is consistent with similar instructions endorsed by many courts
    over a period of decades. But consistency and accuracy are distinct.
    Courts can be consistently wrong.
    UNITED STATES V. FLUCAS                    57
    II
    People are complex. We are pulled by competing
    interests, representing people, events, and circumstances.
    Some choices in life are mutually exclusive. We can attend
    the symphony or go the movies. We can’t do both at the
    same time. But many times, we can accommodate more than
    one interest—we pick up the dry cleaning on our way home
    from grocery shopping. We go to the university library to
    begin research on a term paper, but that is also where our
    friends are hanging out tonight, and it is quieter than staying
    in the dorm. And we are capable of holding in our minds
    multiple reasons for our choices. But not every reason is as
    important as every other reason. Figuring out what moves us
    is one of the joys and terrors of life. It is also core to
    determining mens rea.
    A
    “Dominant,” “significant,” and “motivating” are three
    ways of expressing different degrees of influence on a
    person’s decision-making. To my mind, they represent a
    hierarchy of explanations for our decisions. “Dominant”
    means “[e]xercising chief authority or rule: ruling, governing,
    [or] commanding; most influential” and “[o]ccupying a
    commanding position.” Dominant, Oxford English Dictionary
    (2d ed. 1989) (emphasis added). This represents the most
    demanding standard. A dominant purpose would occupy a
    commanding position in an individual’s decision-making
    process. That is, it would be at the forefront of the
    individual’s mind when making the decision. “Significant”
    means “[s]ufficiently great or important to be worthy of
    attention; noteworthy; consequential, influential” or
    “noticeable, substantial, considerable, large.” Significant,
    58               UNITED STATES V. FLUCAS
    Oxford English Dictionary (2d ed. 1989). This is, admittedly,
    not an obvious or large step down from dominant. But it does
    capture an important idea—a purpose need not be the
    dominant purpose, but it must bear some significance in our
    decision. In other words, it should be a dominant purpose,
    even if it is not the dominant purpose.
    By contrast, “motivate” means “[t]o provide or serve as
    a rationale for (some action, etc.); to justify.” Motivate,
    Oxford English Dictionary (2d ed. 1989). This conveys little
    sense of comparative weight or importance in the decision-
    making process. A factor can play a small role in a person’s
    decision-making and still motivate them. If we are going to
    the grocery store because we have no food in the house for
    dinner, stopping at the dry cleaners might be useful if it is on
    the way; it supplies an additional motive for the trip, even if
    it is not so important as to justify a separate trip. Picking up
    the dry cleaning provides additional value to the trip to the
    store. That may help motivate us to go (or to go now, before
    the dry cleaners closes) without being the dominant or even
    a significant reason for leaving the house. If we are not in
    hurry to collect the dry cleaning, it may be entirely incidental
    to our reasons for going out. Even our grocery shopping has
    its own set of priorities. We need milk, bread, and eggs, but
    we also pick up a frozen pizza and a Midnight Milky Way.
    Does each of these items motivate us? Are they of equal of
    value? Is one or more of the items the dominant reason? A
    significant reason?
    I don’t think that “motivating” can bear the same weight
    as either “dominant” or “significant.” It may carry such
    weight, but it does not necessarily carry the same weight.
    Here is how we test that.
    UNITED STATES V. FLUCAS                               59
    Following Mortensen, federal courts added to their
    instructions the caveat that the government did not have to
    prove that crossing state lines for illicit purposes was “the
    dominant purpose” for the trip; it was sufficient if it was “a
    dominant purpose.” Similarly, it doesn’t do violence to the
    rule to say that the government doesn’t have to prove that
    interstate travel for illicit purposes was not “the significant
    purpose,” but only “a significant purpose.” As a matter of
    ordinary conversation, it is also easy to see how we
    might—in our effort to provide more word clues for the
    jury—think that the government also does not have to prove
    that interstate travel was “the motivating purpose,” but only
    “a motivating purpose.” But here is where those formulations
    break down. Once the jury is told that travel must be “a
    motivating purpose,” it is a short step for the jury to think that
    the government satisfies its burden if it has proven that
    interstate travel for illicit purposes was any motivating
    purpose, no matter how insignificant.8 Indeed, “dominant”
    and “significant” are frequently used as modifiers before
    some variant of “motivating” in order to emphasize that not
    any motivation will satisfy the criteria under examination.
    See, e.g., American Legion v. American Humanist Ass’n,
    
    139 S. Ct. 2067
    , 2085 (2019) (“This is not to say that the
    8
    Instructing the jury that traveling across state lines for illicit sexual
    activity may not be “merely incidental” to the trip is not sufficient to
    overcome this error. “Incidental” means “[o]ccurring or liable to occur in
    fortuitous or subordinate conjunction with something else of which it
    forms no essential part; casual.” Incidental, Oxford English Dictionary (2d
    ed. 1989). Thus, to say that illicit sexual activity may not be “merely
    incidental” tells the jury that it must have played, at a minimum, some
    minor role beyond fortuity in the decision to make the trip. That
    represents a significant departure from the “dominant purpose” test
    expounded by the Supreme Court in Mortensen and that we adopted in
    Fox.
    60               UNITED STATES V. FLUCAS
    cross’s association with the war was the sole or dominant
    motivation for the inclusion of the symbol in every World
    War I memorial that features it.”); Pena-Rodriguez v.
    Colorado, 
    137 S. Ct. 855
    , 867 (2017) (“The Court must
    decide whether the Constitution requires an exception to the
    no-impeachment rule when a juror's statements indicate that
    racial animus was a significant motivating factor in his or her
    finding of guilt.”); Palmer v. Thompson, 
    403 U.S. 217
    , 225
    (1971) (“It is difficult or impossible for any court to
    determine the ‘sole’ or ‘dominant’ motivation behind the
    choices of a group of legislators.”).
    The hierarchy of terms I have proposed here is reflected
    in United States v. Generes, 
    405 U.S. 93
     (1972). It is a tax
    case, and the particulars are not important to us. But the case
    “turn[ed] on the proper measure of the required proximate
    relation” between a bad debt and the taxpayer’s business. 
    Id. at 96
    . The court had to determine whether “this necessitate[s]
    a ‘dominant’ business motivation on the part of the taxpayer,
    or is a ‘significant’ motivation sufficient?” 
    Id. at 96
    . In
    posing the question, the Court implicitly recognizes that there
    is a distinction between these two terms. Ultimately, the
    Court held that a proof of a significant motivation is different
    from proof of a dominant motivation. “We conclude that . . .
    the proper measure is that of dominant motivation, and that
    only significant motivation is not sufficient.” 
    Id. at 103
    . By
    the Supreme Court’s reasoning, any “motivation” is certainly
    an even lower bar than either qualifier that the Court
    considered.
    Similarly, in United States v. Miller, a Mann Act case
    from the Second Circuit, Miller argued that the Act requires
    proof that criminal sexual activity was “the dominant
    purpose.” 
    148 F.3d 207
    , 211 (2d Cir. 1998). The court
    UNITED STATES V. FLUCAS                  61
    rejected the argument. In the process, the Second Circuit
    used “motivation” and “purpose” interchangeably and
    explained why one could have more than one dominant
    purpose for an act:
    [I]n everyday speech we can and do describe
    groups as “dominant.” For example, it makes
    perfect sense to discuss the “dominant
    companies” in an industry or the “dominant
    teams” in a league, and all we mean by
    describing these companies or teams as
    “dominant” is that they are relatively more
    successful or influential than others.
    Likewise, in the context of multiple purposes,
    “dominant” simply means that these
    motivations predominate over other, less
    powerful motivations for conduct.
    
    Id. at 212
    . If “a motivating purpose” will satisfy the Mann
    Act, we will have no reason to ask the jury whether “these
    motivations predominate over other less powerful
    motivations for conduct”—because any motivating purpose
    will do.
    B
    This analysis is confirmed in the 2018 amendments to the
    current version of the Mann Act. The 2018 amendment to
    Section 2423(b) makes clear what the dictionary definitions
    suggest—“motivating” is a lesser standard than “dominant”
    or “significant.” Section 2423, a derivative of Section 4 of
    the Mann Act, provides harsh penalties for transporting
    minors to engage in illicit sexual activity. Compare
    
    18 U.S.C. § 2421
    (a) (providing for sentences of “not more
    62                  UNITED STATES V. FLUCAS
    than 10 years”) with 
    id.
     § 2423(a) (providing for sentence of
    “not less than 10 years or for life”); id. 2423(b) (providing for
    sentence of “not more than 30 years).9 Prior to 2018,
    § 2423(b) made it a crime for “[a] person [to] travel[] in
    interstate commerce or travel[] into the United States . . . for
    the purpose of engaging in any illicit sexual conduct.” In
    2018, Congress amended § 2423(b) to make one small
    change. The current version of § 2423(b) reads, “A person
    who travels in interstate commerce or travels into the United
    States . . . with a motivating purpose of engaging in any illicit
    sexual conduct with another person . . . .” 
    18 U.S.C. § 2423
    (emphasis added). “With a motivating purpose,” replaced
    “for the purpose of” in the prior iteration of the statute.
    Critically, Congress did not amend any other sections of the
    Mann Act, including the two provisions under which Flucas
    was convicted—§§ 2421(a), 2423(a). Prior to the 2018
    amendment, most federal courts had treated § 2423(b) similar
    to §§ 2421(a) and 2423(a) and had used “dominant” and
    “significant” as the qualifiers for “purpose.” See Schneider,
    801 F.3d at 194; McGuire, 
    627 F.3d at
    624–25; Vang,
    
    128 F.3d at
    1072–73; but see United States v. Garcia-Lopez,
    
    234 F.3d 217
    , 219–20 (5th Cir. 2000) (holding it was not
    error for the district court to refuse to give “a significant or
    dominant purpose” instruction and instead instruct that it was
    “enough if one of the defendant’s motives in traveling in
    foreign commerce was to engage in a sexual act with a
    minor”).
    9
    Section 2423 applies to crimes involving minors. Section 2423(a),
    which has language nearly identical to 2421(a), punishes persons who
    transport minors “with intent that the individual engage in engage in
    prostitution, or in any sexual activity for which any person can be charged
    with a criminal offense.” Section 2423(b) punishes person who travel to
    engage in illicit sexual conduct. Section 2423(b) does not require that the
    defendant have transported anyone.
    UNITED STATES V. FLUCAS                               63
    Why did Congress tinker with the language? The statute
    was amended as part of the Abolish Human Trafficking Act
    of 2017 to make it easier to convict sex tourists. While
    §§ 2421(a) and 2423(a) punish those who transport persons
    for illicit sex, § 2423(b) punishes those who travel for illicit
    sex. As a legislative summary explained: “In order to help
    curb foreign offenders and internal [sic] human trafficking,
    the legislation clarifies that persons who travel overseas with
    a motivating purpose of engaging in illicit sex tourism can be
    federally prosecuted for their offense.” Cornyn, Klobuchar
    Bill to Fight Human Trafficking Signed into Law, East
    Texas Review (Dec. 22, 2018) (emphasis added),
    https://easttexasreview.com/cornyn-klobuchar-bill-fight-hu
    man-trafficking-passes-senate/. Congress’s concern with sex
    tourism is understandable in context. Whereas §§ 2421(a)
    and 2423(a) punish one who “knowingly transports” a victim
    across state lines for a particular purpose—a deliberate act
    involving at least two people—§ 2423(b) punishes mere
    “travel” across a border with bad intent. It makes sense for
    Congress to try to reach a sex tourist who comes to the United
    States with mixed motives—to see the Empire State Building
    and the Grand Canyon and also to have illicit sex. In that
    situation, Congress might well try the outer boundaries of its
    authority to punish any “motivating purpose” for travelers,
    but be satisfied with the historic limits—a “dominant” or
    “significant” purpose—when it comes to persons who
    knowingly transport others for immoral purposes.10 By
    10
    Section 2423(c) has lowered the bar to prosecution even more. It
    makes it illegal to travel in foreign commerce “and engage[] in any illegal
    sexual conduct.” 
    18 U.S.C. § 2423
    (c). No proof of intent or motive is
    required; it is a strict liability statute. United States v. Pepe, 
    895 F.3d 679
    ,
    688 n.4 (9th Cir. 2018) (“[Section] 2423(c) doesn’t itself require a mens
    rea . . . .”). See Sex Tourism Prohibition Improvement Act of 2002, H.R.
    Rep. No. 107-525, at 3 (The bill “eliminates the intent requirement”), 5
    64                  UNITED STATES V. FLUCAS
    making “motivating purpose” the standard in § 2423(b),
    Congress lowered the government’s burden of proof for
    conviction. The 2018 amendment removes any possibility
    that a jury may acquit if the defendant’s purpose was not a
    dominant or significant one. By not amending §§2421(a) and
    2423(a) at the same time, Congress left the higher burden of
    proof in place.
    III
    My concerns are not mere classroom hypotheticals.
    When the district court added that word “motivating” to the
    jury instruction, it lowered the government’s burden of proof.
    At Flucas’s second trial, the jury was told that it was
    sufficient if the government has proven that “the sexual
    activity was a significant, dominant, or motivating purpose”
    for Flucas’s move to California. We should not be surprised
    that the jury thought that it could convict Flucas if the sexual
    activity was “any motivating purpose” for his travel from
    Oregon to California. That is a clear departure from the
    Supreme Court’s decision in Mortensen.
    The district court’s decision to add “or motivating” to the
    instruction plainly was a critical change from the first trial to
    the second. The government didn’t request it idly, and
    Flucas’s counsel promptly objected and identified the
    (2002). I note that the 2002 bill did not pass, but it became the basis for
    later amendments. See Sara Sun Beale, Prosecuting Sexual Exploitation
    and Trafficking Abroad: Congress, the Courts, and the Constitution,
    27 Duke J. Gender L. & Pol’y 25, 26–27, 27 n.12 (2020).
    UNITED STATES V. FLUCAS                            65
    problem for the district court.11 When the second jury was
    told it could find Flucas guilty if “the [illegal] sexual activity
    was a significant, dominant, or motivating purpose,” only one
    of those needed be true to convict because the instruction was
    phrased in the disjunctive. That gave the jury a choice of
    standards, and we must assume that it chose the common
    denominator—“motivating”—because satisfying that
    standard would automatically satisfy the higher standards of
    “dominant” and “significant.”12 The instruction thus
    improperly lowered the bar from the required intent—a
    dominant or significant purpose.
    That reduced standard could have made a difference here,
    one that we cannot conclude was harmless beyond a
    reasonable doubt. See McDonnell v. United States, 
    136 S. Ct. 2355
    , 2375 (2016); Chapman v. California, 
    386 U.S. 18
    , 24
    (1967). The evidence in this case must have been difficult to
    hear. Flucas testified at trial and he admitted to having sex
    11
    Counsel for Flucas explained his objection to the district court: “I
    think significant and dominant are equal. Motivating is lower. And
    incidental is even lower than that. So I think that motivating is—just
    means something totally different than significant or dominant.” He
    advised the court that “significant” and “dominant” had been approved in
    prior cases, “but the motivating is a new—a new word put in there.”
    12
    The majority refers to my point as a “speculative assertion.” Maj.
    Op. 13 n.6. I am not sure why that is significant. We never know what
    the basis for a jury’s decision is. We assume that juries follow their
    instructions. United States v. Mitchell, 
    502 F.3d 931
    , 990 (9th Cir. 2007).
    “We cannot know what this jury did behind closed doors. The standard
    the jury applied can only be gleaned from examining what the jury was
    told.” Chalmers v. Mitchell, 
    73 F.3d 1262
    , 1267 (2d Cir. 1996). Flucas’s
    jury was provided with a disjunctive, and one of the alternatives is
    erroneous. We have to assume that the jury followed the district court’s
    instruction and decided on the basis of the bad instruction.
    66               UNITED STATES V. FLUCAS
    with at least one of his daughters and a stepdaughter and
    fathering children by them. There was also very strong
    evidence that Flucas had repeatedly had sex with his
    daughters and others over a long period, including his time in
    Georgia, his stay in Oregon, and after his move to California.
    And the government elicited from Flucas that he knew what
    he had done was wrong and that he had considered fleeing the
    country. But the evidence that illicit sexual conduct with his
    daughters and other young women was a dominant or
    significant reason Flucas moved his family from Oregon to
    California was flimsy. Flucas was settled in Klamath Falls,
    Oregon, where he had a job with the school district that
    worked out to about $18 per hour. In addition to his salary,
    he received another $10,000 to compensate him for his
    mileage. Flucas had asked the Klamath school district for
    more money, but the district told him there would be no bump
    in salary and that it planned to reduce his mileage
    compensation. In the meantime, the Stockton Unified School
    District made him a better offer, one that would work out to
    about $31 per hour, plus compensation for his mileage. It
    would be more money for fewer hours. In addition, the
    school district offered his wife a salaried position as well,
    also working with hearing-impaired students.
    So why did Flucas move to California? To take a new
    job, as the defense argued? Or to continue to sexually abuse
    his children, as the government claimed? The choices are not
    mutually exclusive, but they do require some assessment of
    the relative weight of Flucas’s motives for accepting a new
    teaching position and moving his family. But without
    considering the relative weight of his reasons for moving, the
    jury may be very tempted to punish Flucas because (1) he
    crossed a state line and (2) he was a serial sexual abuser. But
    traveling across a state line while a serial sex abuser is not
    UNITED STATES V. FLUCAS                    67
    sufficient for a conviction under the Mann Act. Being a serial
    sexual abuser describes one’s status, not a purpose for
    crossing a state line. There is a serious doubt that Flucas
    crossed the Oregon-California border with his family and
    moving truck as “calculated means for effectuating sexual
    immorality.” Mortensen, 332 U.S. at 375.
    ****
    One final, broader observation. The Mann Act is a
    parasitic act because it depends on violations of the laws of
    non-federal jurisdictions. The Act punishes “any sexual
    activity for which any person can be charged with a criminal
    offense.” 
    18 U.S.C. § 2421
    (a). Sex crimes are traditionally
    defined by state law. That means that the interstate
    transportation element is the only thing that narrows the
    Mann Act; otherwise, federal law would be at least
    coextensive with state law. This should concern us. “[G]iven
    the structure of our federal criminal justice system, we would
    expect that state laws criminalizing sexual activity with
    minors would encompass a broader range of conduct than
    federal laws.” United States v. McCauley, 
    983 F.3d 690
    , 696
    (4th Cir. 2020). We should hesitate long before we attribute
    to Congress an exercise of power to displace the states in this
    traditional area of state control. See United States v. Lopez,
    
    514 U.S. 549
    , 564 (1995) (warning that the “implications of
    the Government’s arguments” make it “difficult to perceive
    any limitation on federal power . . . in areas such as criminal
    law enforcement . . . where States historically have been
    sovereign.”). “When charged conduct does not fall in the
    heartland of [the Mann Act’s] proscription, the risk of
    prejudice becomes more palpable.” McCauley, 983 F.3d
    at 698. This is not to say that Flucas’s “conduct was in any
    way excusable or beyond the reach of the criminal law. It is
    68                UNITED STATES V. FLUCAS
    simply that it is quite possible that properly instructed the
    jury would find this defendant’s conduct falls outside” of
    federal criminal jurisdiction. Id.
    IV
    I would reverse the judgment of conviction and remand
    to the district court with instructions that if the government
    wishes to retry Flucas, the jury must be instructed that his
    continued illicit sexual conduct was one of the dominant or
    significant purposes for moving his family from Oregon to
    California.
    For these reasons, I respectfully dissent.