                    FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                      No. 10-30072
                Plaintiff-Appellee,                D.C. No.
               v.                              1:09-cr-00023-
MARK STEVEN ELK SHOULDER,                           JDS-1
             Defendant-Appellant.
                                                 OPINION

        Appeal from the United States District Court
                for the District of Montana
     Jack D. Shanstrom, Senior District Judge, Presiding

                    Submitted June 1, 2012*
                       Portland, Oregon

                     Filed October 5, 2012

       Before: A. Wallace Tashima, Carlos T. Bea, and
               Sandra S. Ikuta, Circuit Judges.

                     Opinion by Judge Ikuta




  *The panel unanimously concludes this case is suitable for decision
without oral argument. See Fed. R. App. P. 34(a)(2).

                               12119
12122          UNITED STATES v. ELK SHOULDER


                         COUNSEL

Lisa J. Bazant, Billings, Montana, for the appellant.

Marcia Hurd, Office of the United States Attorney, Billings,
Montana, for the appellee.


                         OPINION

IKUTA, Circuit Judge:

   This appeal challenges the constitutionality of certain key
provisions of the Sex Offender Registration and Notification
Act (SORNA). Pub. L. 109-248, Tit. I, 120 Stat. 590 (2006)
(codified in scattered sections of the U.S.C.). Defendant Mark
Steven Elk Shoulder was prosecuted under 18 U.S.C.
§ 2250(a) for failing to comply with the sex offender registra-
tion requirements set forth in 42 U.S.C. § 16913. He now
argues that his conviction was invalid, because SORNA vio-
lates the Ex Post Facto Clause and the Due Process Clause,
and because Congress lacked the constitutional authority to
                    UNITED STATES v. ELK SHOULDER                       12123
enact SORNA. We reject these constitutional challenges, and
affirm the judgment of the district court.

                                       I

   SORNA was enacted in response to “Congress’ awareness
that pre-[SORNA] registration law consisted of a patchwork
of federal and 50 individual state registration systems.” Reyn-
olds v. United States, 132 S. Ct. 975, 978 (2012) (citing 73
Fed. Reg. 38045 (2008)). SORNA sought to improve the uni-
formity and effectiveness of those systems by, among other
things, “creating federal criminal sanctions applicable to those
who violate the Act’s registration requirements.” Id. To effec-
tuate this goal, SORNA’s registration requirement, 42 U.S.C.
§ 16913, requires all state and federal sex offenders, as defined,1
to “register, and keep the registration current, in each jurisdic-
tion where the offender” resides, works, or goes to school.2 A
person who fails to register as required by § 16913 may be
criminally prosecuted under 18 U.S.C. § 2250(a). This provi-
sion requires the government to prove that the defendant: (1)
is required to register under SORNA, (2) is a “sex offender”
as defined due to a conviction under federal law (or the law
of certain other listed jurisdictions) or a person who “travels
in interstate or foreign commerce, or enters or leaves, or
  1
     42 U.S.C. § 16911(1) provides: “The term ‘sex offender’ means an
individual who was convicted of a sex offense.” The term “sex offense”
is defined in § 16911(5)(A)(i) to include: “a criminal offense that has an
element involving a sexual act or sexual contact with another.”
   2
     42 U.S.C. § 16913(a) provides:
      A sex offender shall register, and keep the registration current, in
      each jurisdiction where the offender resides, where the offender
      is an employee, and where the offender is a student. For initial
      registration purposes only, a sex offender shall also register in the
      jurisdiction in which convicted if such jurisdiction is different
      from the jurisdiction of residence.
12124              UNITED STATES v. ELK SHOULDER
resides in, Indian country” and, (3) knowingly failed to regis-
ter or update a registration as required by SORNA.3

   These SORNA provisions provide the backdrop to the facts
of this case. In 1991, Elk Shoulder was convicted in a federal
district court in Montana of sexual abuse of a six-year-old
child in violation of 18 U.S.C. § 2241(c).4 Elk Shoulder was
sentenced to 172 months in prison, followed by five years
supervised release. When Elk Shoulder was released in
December 2003, officials informed him that he was required
to register as a sex offender under Montana law. He registered
in Yellowstone County, Montana, where he signed and ini-
tialed the state’s “Sexual and Violent Offender Registration
Form.” By doing so, Elk Shoulder acknowledged that under
state law, he was required to maintain a current and updated
  3
   18 U.S.C. § 2250(a) states:
      (a) In General.— Whoever—
         (1) is required to register under the Sex Offender Registra-
         tion and Notification Act;
         (2)   (A) is a sex offender as defined for the purposes of the
               Sex Offender Registration and Notification Act by rea-
               son of a conviction under Federal law (including the
               Uniform Code of Military Justice), the law of the Dis-
               trict of Columbia, Indian tribal law, or the law of any
               territory or possession of the United States; or
               (B) travels in interstate or foreign commerce, or enters
               or leaves, or resides in, Indian country; and
          (3) knowingly fails to register or update a registration as
          required by the Sex Offender Registration and Notification
          Act;
          shall be fined under this title or imprisoned not more than 10
          years, or both.
   4
     At the time of Elk Shoulder’s conviction, § 2241(c) provided that
“[w]hoever, in the special maritime and territorial jurisdiction of the
United States or in a Federal prison, knowingly engages in a sexual act
with another person who has not attained the age of 12 years, or attempts
to do so, shall be fined under this title, imprisoned for any term of years
or life, or both.” 18 U.S.C. § 2241 (1992).
                UNITED STATES v. ELK SHOULDER              12125
registration and that his duty to register would continue for
the rest of his life, even after the expiration of probation or
parole.

   Weeks later, in February 2004, Elk Shoulder violated the
terms of his supervised release and was sentenced to thirty
months in prison, followed by thirty months of supervised
release. Upon his release from prison a second time in April
2006, he again registered as a sex offender in Yellowstone
County. SORNA was enacted three months later. In August
2006, Elk Shoulder again violated the terms of his supervised
release and was sentenced to another twenty-four months in
prison.

   After his release from prison a third time in May 2008, Elk
Shoulder moved around Montana, living at various times in
the Northern Cheyenne Indian Reservation, Bozeman, Lame
Deer, Billings, and Wolf Point. He did not register as a sex
offender in any of these locales.

   In 2009, Elk Shoulder was indicted under 18 U.S.C.
§ 2250(a) for violating the SORNA registration requirements
in 42 U.S.C. § 16913. Before trial, Elk Shoulder brought two
motions to dismiss the indictment. In the first, he asserted that
SORNA’s registration provision exceeded Congress’s author-
ity under the Commerce Clause. In the second, he claimed
that the retroactive application of these provisions violated the
Ex Post Facto Clause. The district court denied both motions.
After a bench trial, the court found Elk Shoulder guilty
beyond a reasonable doubt. He was sentenced to a term of
thirty months imprisonment, to be followed by five years
supervised release.

  On appeal, Elk Shoulder argues that the district court erred
in rejecting his constitutional challenges to SORNA. We
address each of his arguments in turn.
12126              UNITED STATES v. ELK SHOULDER
                                     II

   We first consider Elk Shoulder’s argument that SORNA’s
statutory scheme for requiring sex offenders to register and
criminalizing certain failures to register violates the Ex Post
Facto Clause.

  [1] The Constitution provides: “No . . . ex post facto Law
shall be passed.” U.S. Const. art. I § 9, cl. 3. As the Supreme
Court has succinctly explained, “[l]egislatures may not retro-
actively alter the definition of crimes or increase the punish-
ment for criminal acts.” Collins v. Youngblood, 497 U.S. 37,
43 (1990); see also United States v. Elkins, 683 F.3d 1039,
1044 (9th Cir. 2012) (holding that the Ex Post Facto Clause
“bars the enactment of any law that imposes a punishment for
an act which was not punishable at the time it was committed;
or imposes additional punishment to that then prescribed.”)
(quoting Russell v. Gregoire, 124 F.3d 1079, 1083 (9th Cir.
1997) (internal quotation marks omitted).

   Elk Shoulder asserts that SORNA’s registration require-
ment constitutes an additional punishment for his federal sex
offense, which he committed in 1991. Because SORNA was
not enacted until 2006, he argues that the Ex Post Facto
Clause prohibited Congress from applying the registration
requirement to him.5

  [2] Elk Shoulder’s argument is foreclosed by our recent
decision in United States v. Elkins. 683 F.3d 1039. In Elkins,
a defendant who had been convicted of a sex offense under
  5
    To the extent Elk Shoulder argues that 18 U.S.C. § 2250 also violates
the Ex Post Facto Clause, his claim is meritless. Elk Shoulder’s criminal
conduct (failing to register following his 2008 release from prison)
occurred after SORNA was enacted in July 2006. Therefore, a conviction
under § 2250 cannot violate the Ex Post Facto clause in Elk Shoulder’s
case. Cf. Miller v. Florida, 482 U.S. 423, 430 (1987) (“A law is retrospec-
tive if it changes the legal consequences of acts completed before its effec-
tive date.” (internal quotation marks omitted)).
                   UNITED STATES v. ELK SHOULDER                     12127
Washington law in 1994 failed to register when he moved
from Washington to California in 2010, and was indicted
under § 2250. Id. at 1041-42. Elkins filed a motion to dismiss
the indictment arguing, among other things, that the require-
ment to register violated the Ex Post Facto Clause in his case
because it was punitive in nature and was based on a prior
conviction that occurred before SORNA was enacted. Id. at
1043-44. We concluded that SORNA’s registration require-
ment was not punitive in nature, and therefore did not violate
Elkins’s constitutional rights. Id. at 1045. We based this con-
clusion on Smith v. Doe, 538 U.S. 84 (2003), in which the
Supreme Court applied a five factor test,6 and concluded that
Alaska’s Sex Offender Registration Act, which is similar to
SORNA in all material ways, was not punitive in nature. Id.
at 105-06. We thus rejected the ex post facto challenge to
SORNA, and in doing so joined all of our sister circuits that
have considered the issue. Elkins, 683 F.3d at 1045.7 Because
Elk Shoulder also argues that SORNA’s registration require-
ment cannot be applied to him because it is punitive in nature,
Elkins’s reasoning is equally applicable to Elk Shoulder.
  6
     The Court’s analysis focused on “whether, in its necessary operation,
the regulatory scheme: [1] has been regarded in our history and traditions
as a punishment; [2] imposes an affirmative disability or restraint; [3] pro-
motes the traditional aims of punishment; [4] has a rational connection to
a nonpunitive purpose; or [5] is excessive with respect to this purpose.”
Smith, 538 U.S. at 97.
   7
     See, e.g., United States v. DiTomasso, 621 F.3d 17, 25 (1st Cir. 2010),
abrogated on other grounds by Reynolds, 132 S. Ct. 975; United States v.
Guzman, 591 F.3d 83, 94 (2d Cir. 2010); United States v. Shenandoah,
595 F.3d 151, 158-59 (3d Cir. 2010), abrogated on other grounds by
Reynolds, 132 S. Ct. 975; United States v. Gould, 568 F.3d 459, 466 (4th
Cir. 2009); United States v. Young, 585 F.3d 199, 202-06 (5th Cir. 2009);
United States v. Felts, 674 F.3d 599, 605-06 (6th Cir. 2012); United States
v. Leach, 639 F.3d 769, 772-73 (7th Cir. 2011); United States v. May, 535
F.3d 912, 919-20 (8th Cir. 2008), abrogated on other grounds by Reyn-
olds, 132 S. Ct. 975; United States v. Hinckley, 550 F.3d 926, 935-38
(10th Cir. 2008), abrogated on other grounds by Reynolds, 132 S. Ct. 975;
United States v. W.B.H., 664 F.3d 848, 852-60 (11th Cir. 2011).
12128           UNITED STATES v. ELK SHOULDER
   Despite this precedent, Elk Shoulder argues that the Court’s
analysis in Smith “no longer hold[s] true in today’s society,”
and the purpose and effect of SORNA’s registration require-
ment is punitive in nature. Elk Shoulder focuses on the
Supreme Court’s holding that the Alaska registration statute
does not resemble shaming punishments of the colonial period
(the first factor of Doe’s five-factor test), and that there was
“no evidence that [the registration requirement] has led to
substantial occupational or housing disadvantages for former
sex offenders that would not have otherwise occurred through
the use of routine background checks by employers and land-
lords.” 538 U.S. at 100 (the second factor). According to Elk
Shoulder, today SORNA’s registration requirement imposes
significant hardships on offenders, who are “held to public
ridicule by community members,” and face difficulty finding
and maintaining both employment and housing. He notes that
local newspapers frequently maintain interactive maps of the
registered residences of sex offenders, and cites “reports of
incidents of citizens standing on street corners bearing signs
with the names and addresses of offenders blaz[o]ned across
the front.”

   This argument fails. Most important, we have recently reaf-
firmed the nonpunitive nature of SORNA in Elkins, which we
are bound to follow. Miller v. Gammie, 335 F.3d 889, 899
(9th Cir. 2003) (en banc). Further, Smith v. Doe contemplated
that information from the Alaska sex registration statute
would be available on the internet, but determined that such
internet notification was nonpunitive because its principal
effect was to “inform the public for its own safety, not to
humiliate.” 583 U.S. at 99. The Court further noted that there
was no evidence that the Alaska act had “led to substantial
occupational or housing disadvantages that would not have
otherwise occurred through the use of routine background
checks by employers and landlords.” Id. at 100. Because
“only the clearest proof will suffice to override legislative
intent and transform what has been denominated a civil rem-
edy into a criminal penalty,” id. at 92 (internal citation and
               UNITED STATES v. ELK SHOULDER             12129
quotation marks omitted), Elk Shoulder’s conclusory state-
ments and handful of anecdotal examples cannot carry the
heavy burden of showing substantial changes in society that
would require us to revisit the Supreme Court’s conclusion.

   [3] We thus reject Elk Shoulder’s argument that applica-
tion of the SORNA registration requirements to him on the
basis of his earlier conviction violates the Ex Post Facto
Clause.

                              III

   [4] We next turn to Elk Shoulder’s arguments that
SORNA’s registration requirement violates his rights under
the Fifth Amendment, which bars the federal government
from depriving persons of “life, liberty, or property, without
due process of law.” U.S. Const. amend. V.

   Elk Shoulder first asserts that he was deprived of his right
to due process because it was impossible for him to comply
with SORNA. As noted above, in order to convict Elk Shoul-
der under § 2250(a), the government had to prove that Elk
Shoulder knowingly failed “to register or update a registration
as required by” SORNA. § 2250(a)(3) (emphasis added). Elk
Shoulder points out that SORNA required states to adopt the
new procedures for sex offender registries established by the
Act, or lose part of their federal funding. 42 U.S.C.
§§ 16924(a), 16925. Elk Shoulder argues that, because Mon-
tana had not yet conformed its sex offense registry to
SORNA’s requirements, it was impossible for him to register
“as required by” SORNA.

   [5] We have previously rejected this argument, both in
United States v. George, 625 F.3d 1124, 1128-29 (9th Cir.
2010), vacated on other grounds, 672 F.3d 1126 (9th Cir.
2012), and in Elkins, 683 F.3d at 1046. As we stated in Elkins,
“the federal government’s prosecution of an alleged violation
of SORNA is not dependent on the individual state’s imple-
12130           UNITED STATES v. ELK SHOULDER
mentation of the administrative portion of SORNA.” Elkins,
683 F.3d at 1046; accord id. at 1046 n.9 (the “duty to register
in a state registry is independent of a state’s degree of imple-
mentation of SORNA.” (quoting Felts, 674 F.3d at 603)); see
also Guzman, 591 F.3d at 93; Gould, 568 F.3d at 464.
Because Elk Shoulder could have registered with the State of
Montana’s registry, and because this would have allowed him
to register “as required by” SORNA, it was not impossible for
Elk Shoulder to meet the requirements of § 2250(a). Thus,
this case presents no impossibility-based due process prob-
lems.

   [6] Second, Elk Shoulder asserts that he did not receive
notice that failure to register as a sex offender would violate
SORNA, and therefore he did not receive notice sufficient to
comply with the Due Process Clause. This argument is merit-
less. In order to convict a defendant under § 2250(a), “the
government [must] prove that a convicted sex offender knew
of a registration requirement and knowingly failed ‘to register
or update a registration.’ ” United States v. Crowder, 656 F.3d
870, 876 (9th Cir. 2011) (quoting § 2250(a)(3)). A SORNA
defendant’s knowledge of his failure to “register or update a
registration” as required by state law is sufficient to satisfy the
“notice” requirement of the Due Process Clause. Elkins, 683
F.3d at 1049-50; accord United States v. Brown, 586 F.3d
1342, 1351 (11th Cir. 2009) (“[W]e join our sister circuits in
concluding that ‘notice of a duty to register under state law is
sufficient to satisfy the Due Process Clause.” (internal quota-
tion marks omitted)). The defendant need not know that the
same failure also violates SORNA. Thus, because Elk Shoul-
der received notice of his obligation to register under Mon-
tana state law, he received all the notice the Due Process
Clause requires.

                                IV

  [7] Finally, Elk Shoulder argues that Congress lacks the
Constitutional authority to punish his failure to register under
                   UNITED STATES v. ELK SHOULDER                     12131
SORNA. At issue is whether Congress has the authority to
impose SORNA registration requirements on individuals who,
like Elk Shoulder, are convicted of federal sex crimes.8

   “The Federal Government ‘is acknowledged by all to be
one of enumerated powers.’ ” Nat’l Fed’n of Ind. Bus. (NFIB)
v. Sebelius, 132 S. Ct. 2566, 2576 (2012) (quoting McCulloch
v. Maryland, 17 U.S. (4 Wheat.) 316, 405 (1819)). No clause
in Article I expressly authorizes Congress to impose registra-
tion requirements on federal convicts such as Elk Shoulder.
Nevertheless, the government argues that because Congress
had authority to enact § 2241(c) (Elk Shoulder’s statute of
conviction) under the Constitution’s Property Clause, U.S.
Const., art. IV, § 3, cl. 2,9 Congress also had the authority to
enact §§ 16913 and 2250(a) under the Necessary and Proper
Clause, which empowers Congress “[t]o make all laws which
shall be necessary and proper for carrying into Execution the
foregoing Powers, and all other Powers vested by this Consti-
tution in the Government of the United States,” U.S. Const.
art. I, § 8, cl. 18.

                                    A

   The Supreme Court provided a framework for analyzing
such arguments in United States v. Comstock, 130 S. Ct. 1949
(2010). In Comstock, the Court upheld a civil commitment
statute that allowed the government to detain, past their
release dates, sexually dangerous individuals who were
already in federal custody, as a valid use of Congress’s power
   8
     Because Elk Shoulder was convicted of a sex offense under federal
law, we do not reach his argument that SORNA’s imposition of registra-
tion requirements on sex offenders convicted under state law exceeded
Congress’s power under the Commerce Clause.
   9
     “The Congress shall have Power to dispose of and make all needful
Rules and Regulations respecting the Territory or other Property belong-
ing to the United States; and nothing in this Constitution shall be so con-
strued as to Prejudice any Claims of the United States, or of any particular
State.” U.S. Const., art. IV, § 3, cl. 2.
12132           UNITED STATES v. ELK SHOULDER
under the Necessary and Proper Clause. Id. at 1954. In ana-
lyzing this issue, the Court weighed five considerations, id. at
1956, which (it was careful to explain), did not constitute a
test to be satisfied, id. at 1965. As explained in more detail
below, these considerations included whether the Congressio-
nal enactment: (1) was rationally related to the implementa-
tion of a constitutionally enumerated power; (2) was “a
modest addition” to existing federal legislation; (3) was rea-
sonably adapted to its ends; (4) accommodated state interests
and state sovereignty; and (5) was not “too sweeping in
scope,” and was linked to a constitutionally enumerated
power in a manner that was not too attenuated. Id at 1956-65.

   Comstock’s analysis of these five factors is directly applica-
ble to the SORNA registration statute.

   First, Comstock determined that the civil commitment stat-
ute at issue in that case was rationally related to the constitu-
tionally enumerated powers that authorized Congress to enact
and enforce laws. Id. at 1956. The Court reasoned that
because Congress had the power to “ensure the enforcement
of federal criminal laws enacted in furtherance of its enumer-
ated powers,” id. at 1958, it likewise “can cause a prison to
be erected at any place within the jurisdiction of the United
States,” and direct that it be used for the imprisonment of fed-
eral criminals. Id. (quoting Ex parte Karstendick, 93 U.S. 396,
400 (1876)) (internal quotation marks omitted). Congress,
“having enacted a prison system, can enact laws that seek to
ensure that system’s safe and responsible administration.”
Comstock, 130 S. Ct. at 1958. It may also seek to “ensure the
safety of . . . those in the surrounding communities” with the
enactment of further criminal laws. Id. Each link in this chain,
the Court explained, is rationally related to the underlying
enumerated power; the powers authorizing the prisoners’ stat-
utes of conviction. By extension, this gave Congress the
authority to confine “mentally ill and sexually dangerous per-
sons who are already in federal custody, even if doing so
                UNITED STATES v. ELK SHOULDER             12133
detains them beyond the termination of their criminal sen-
tence.” Id. at 1961.

   [8] We apply Comstock’s analysis here. The parties do not
dispute that Congress had the power to enact § 2241(c), Elk
Shoulder’s crime of conviction, under the Property Clause.
This constitutional authority gave Congress the power to
enact laws to ensure the safety of the surrounding communi-
ties by regulating and monitoring post-release behavior. See
Comstock, 130 S. Ct. at 1958. SORNA’s registration require-
ment, see § 16913, and the criminal penalties for the violation
of the registration requirements, see § 2250, are rationally
related to public safety, “which is advanced by alerting the
public to the risk of sex offenders in their community,” Smith,
538 U.S. at 102-03. Accordingly, SORNA was rationally
related to an enumerated power.

   [9] Second, Comstock determined that the civil commit-
ment statute was “a modest addition to a set of federal prison-
related mental-health statutes that ha[d] existed for many dec-
ades.” Id. at 1958, 1961. The same conclusion is applicable
here. Requiring sex offenders to register and update their
addresses is “a modest addition” to the federal government’s
long history of regulating federal offenders after their release
from incarceration through probation, parole and supervised
release. See, e.g., Sentencing Reform Act of 1984, Pub. L.
No. 98-473, 98 Stat. 1987; Act of June 25, 1910, 36 Stat. 819
(establishing parole for federal prisoners). Federal law has
required states to maintain sex offender registration and com-
munity notification systems since 1994. See Carr v. United
States, 130 S. Ct. 2229, 2233 (2010). A registration require-
ment “imposes the more minor condition of registration,”
Smith, 538 U.S. at 104, compared to the custodial require-
ments of parole, probation, and supervised release.

   [10] Third, Comstock held that the civil commitment stat-
ute at issue was reasonably adapted to its ends. Among other
things, “Congress could have reasonably concluded that fed-
12134          UNITED STATES v. ELK SHOULDER
eral inmates who suffer from a mental illness that causes them
to have serious difficulty in refraining from sexually violent
conduct, would pose an especially high danger to the public
if released.” Comstock, 130 S. Ct. at 1961 (internal citation
and quotation marks omitted). Here, Congress’s decision to
enact SORNA to enhance public safety by imposing a regis-
tration requirement on convicted federal sex offenders and
criminalizing the failure to register, is also “reasonably
adapted to the attainment of a legitimate end,” id. at 1957
(internal quotation marks omitted), namely to “protect the
public from sex offenders and offenders against children,” 42
U.S.C. § 16901, by improving the “patchwork of federal and
. . . state registration systems” that pre-dated SORNA, Reyn-
olds, 132 S. Ct. at 978 (citing 73 Fed. Reg. 38045). Congress
determined that the deficiencies in the pre-SORNA systems
“had enabled sex offenders to slip through the cracks” result-
ing in some 100,000 “missing” sex offenders, and that
SORNA’s comprehensive registries, public notification, infor-
mation sharing and dissemination, and criminal enforcement
penalties, Carr, 130 S. Ct. at 2240-41, are reasonable means
for addressing this problem, see id., at 2238. Further, because
SORNA registration requirements are imposed only on indi-
viduals who were convicted of sexual offenses, it regulates
only “those who by some preexisting activity bring them-
selves within the sphere of federal regulation.” NFIB, 132 S.
Ct. at 2592.

   [11] Fourth, Comstock determined that the civil commit-
ment statute “properly accounts for state interests,” and does
not “invade state sovereignty or otherwise improperly limit
the scope of powers that remain with the States.” Id. at 1962
(internal quotation marks omitted). SORNA likewise reason-
ably accommodates state interests. Although Congress gave
the states primary responsibility in supervising sex offenders,
SORNA is applicable only to federal sex offenders, over
whom the federal government has a “direct supervisory inter-
est,” and those state offenders “who threaten the efficacy of
the statutory scheme by traveling in interstate commerce,”
                UNITED STATES v. ELK SHOULDER             12135
thus placing themselves outsides of the state’s reach. Carr,
130 S. Ct. at 2238-39.

   Additionally, SORNA’s requirement that states implement
SORNA-compliant registration and notification systems in
order to receive certain funds, see 42 U.S.C. § 16925, does
not improperly invade state interests. A state that fails to
“substantially implement” the requirement of SORNA may
lose ten percent of federal funding under the Omnibus Crime
Control and Safe Streets Act of 1968. § 16925(a). This finan-
cial loss is a “relatively mild encouragement” rather than “a
gun to the head.” NFIB, 130 S. Ct. at 2604 (striking down leg-
islation conditioning “over 10 percent of a State’s overall
budget” on state expansion of Medicaid programs). Indeed, as
of July 27, 2011, the statutory deadline for jurisdictions to
implement SORNA, only 14 states had done so. See Melissa
Hamilton, Public Safety, Individual Liberty, and Suspect Sci-
ence: Future Dangerousness Assessments and Sex Offender
Laws, 83 Temp. L. Rev. 697, 706 n.53 (2011).

   [12] Fifth, Comstock held that the links between Con-
gress’s enumerated powers and the federal civil commitment
statute “are not too attenuated.” 130 S. Ct. at 1963. The Court
rejected the argument that “when legislating pursuant to the
Necessary and Proper Clause, Congress’s authority can be no
more than one step removed from a specifically enumerated
power.” Id. Rather, the Court explained, its precedents allow
for many links in the chain. Here, the links between Con-
gress’s enumerated powers and SORNA are no more attenu-
ated than those in Comstock. It is a small step from
Congress’s power to enact laws, criminalize their violation,
place the violators in custody, and protect the public from fed-
eral convicts even after release, see id. at 1964-65, to requir-
ing federal convicts who may be dangerous to the public to
provide information regarding their residences, and punishing
those who fail to do so.

   Further, Comstock concluded that the civil commitment
statute was not “too sweeping in scope.” Id. at 1963. The
12136             UNITED STATES v. ELK SHOULDER
SORNA registration requirements are likewise not “too
sweeping in scope.” Contrary to Elk Shoulder’s assertion that
authorization of lifelong registration requirements would
grant a “general police power” to Congress, the requirement
to register is not nearly as significant a burden as the indefi-
nite detention authorized in Comstock. See id. at 1954-55.
Although the Necessary and Proper Clause provides no justi-
fication for laws effecting “a substantial expansion of federal
authority,” NFIB, 130 S. Ct. at 2592, SORNA’s registration
requirement is “narrow in scope” and “incidental to the exer-
cise” of enumerated powers. Id. at 2592 (opinion of C.J. Rob-
erts) (citations and internal quotation marks omitted).

   [13] Accordingly, we join the Tenth Circuit Court of
Appeals in concluding that SORNA’s registration require-
ment, § 16913, and by extension, the statute penalizing failure
to register, § 2250, were within the scope of Congress’s
authority under the Necessary and Proper Clause. See United
States v. Yelloweagle, 643 F.3d 1275, 1277 (10th Cir. 2011)
(assuming the constitutionality of the registration provision,
and concluding that § 2250 was “a valid exercise of congres-
sional authority under the Necessary and Proper Clause.”);
United States v. Carel, 668 F.3d 1211, 1217 (10th Cir. 2011)
(upholding the constitutionality of § 16913 “[b]ased on Con-
gress’s authority to enact [defendant’s federal] statute of con-
viction” and the Necessary and Proper Clause).

                                    B

   We recognize that the Fifth Circuit has disagreed with this
conclusion, and held that Congress did not have the authority
to require federal convicts who had “been unconditionally
released from federal custody or supervision” before SORNA
was enacted to comply with its registration requirements.10
  10
     Because Elk Shoulder was serving a federally imposed term of super-
vised release when SORNA was enacted in July 2006, Kebedeaux’s spe-
cific holding is not applicable here. We nevertheless consider the logic of
                  UNITED STATES v. ELK SHOULDER                    12137
See United States v. Kebodeaux, 687 F.3d 232, 244, 253 (5th
Cir. 2012). The Fifth Circuit reasoned that “[a]fter the federal
government has unconditionally let a person free, [ ] the fact
that he once committed a crime is not a jurisdictional basis for
subsequent regulation and possible criminal prosecution.” Id.
at 234-35. In effect, the Fifth Circuit deemed the links
between SORNA’s registration requirement and an enumer-
ated Article I power to be per se too attenuated when applied
to federal convicts already released from federal custody. The
Fifth Circuit distinguished Comstock because the civil com-
mitment statute in that case applied to prisoners still in federal
custody. Id. at 236.

   We disagree. The Supreme Court has “made clear that, in
determining whether the Necessary and Proper Clause grants
Congress the legislative authority to enact a particular federal
statute, we look to see whether the statute constitutes a means
that is rationally related to the implementation of a constitu-
tionally enumerated power.” Comstock, 130 S.Ct. at 1956.
Nothing in this jurisprudence supports Kebodeaux’s per se
rule that a Congressional enactment cannot be rationally
related to implementing an enumerated power if it applies to
federal convicts who have been released from custody before
the date of the enactment. Rather, as explained above, a regis-
tration requirement aimed at informing the public of the iden-
tity and location of individuals convicted of sex offenses is
reasonably related to Congress’s authority to ensure the safety
of the public, which in turn flows from its authority to enact

Kebedeaux because, while SORNA was enacted while Elk Shoulder was
on supervised release, SORNA’s registration requirements did not become
applicable to Elk Shoulder until after his unconditional release from
prison in May 2008. See Reynolds, 132 S. Ct. at 978 (holding that
SORNA’s registration requirements “do not apply to pre-Act offenders
until the Attorney General so specifies”); United States v. Valverde, 628
F.3d 1159, 1160 (9th Cir. 2010) (holding that the Attorney General did not
validly specify that SORNA’s registration requirements were retroactive
until August 1, 2008.).
12138           UNITED STATES v. ELK SHOULDER
and enforce criminal laws. Indeed, in Smith v. Doe, the
Supreme Court relied on this reasonable relation between a
registration requirement and a state’s safety objectives in con-
cluding that a state could constitutionally apply its sex
offender registration statute to a person who had been
released from custody before the statute was enacted. See 538
U.S. at 102-03 (agreeing with the appellate court that the stat-
ute had the “legitimate nonpunitive purpose of public safety,
which is advanced by alerting the public to the risk of sex
offenders in their communit[y].”) (internal quotation marks
omitted, alteration in original). While Comstock may be dis-
tinguishable on its facts, we see no reasoned basis for holding
that a law authorizing the federal government to exercise
indefinite civil custody over former federal prisoners even
after they have served their sentences, Comstock, 130 S. Ct.
at 1979 (Thomas, J., dissenting), has less of a rational rela-
tionship to an enumerated power than an enactment requiring
such former federal prisoners to provide registration informa-
tion, even after they have been released from custody.

   Because we reject the Fifth Circuit’s conclusion that Con-
gress cannot “reassert jurisdiction over someone it had long
ago unconditionally released from custody,” Kebodeaux, 687
F.3d at 238, a proposition for which the Fifth Circuit provided
no support, we disagree with its analysis of the Comstock con-
siderations, which it based almost exclusively on that conclu-
sion.

                               V

  [14] Because SORNA violates neither the Ex Post Facto
Clause nor Elk Shoulder’s constitutional right to due process,
and because Congress acted within its enumerated powers in
enacting it, we affirm the judgment of the district court.

  AFFIRMED.
