Congress has sought, to combat sex crimes and crimes against children through sex-offender registration schemes. Congress came to realize that their “loopholes and deficiencies” had allowed over 100,000 sex offenders (about 20% of the total) to escape registration. Congress enacted SORNA. The Act’s express “purpose” is “to protect the public from sex offenders and offenders against children” by “establishing a comprehensive national system for their registration.” SORNA covers more sex offenders and imposes more onerous registration requirements than most States had before. The Act has new criminal penalties. Any person required to register under SORNA who knowingly fails to do so (and who travels in interstate commerce) may be imprisoned for up to ten years. Under the act, the Attorney General shall have the authority to specify the applicability of the requirements to sex offenders convicted before the enactment of SORNA . . . and to prescribe rules for the registration of any such sex offenders and for other categories of sex offenders who are unable to comply. This section focuses on individuals convicted of a sex offense before SORNA’s enactment, the pre-Act offenders. Under that delegated authority, the Attorney General issued an interim rule in February 2007, specifying that SORNA’s registration requirements apply in full to “sex offenders convicted of the offense for which registration is required prior to the enactment of that Act.” The final rule, issued in December 2010, reiterated that SORNA applies to all pre-Act offenders. D is a pre-Act offender. D pleaded guilty under Maryland law for sexually assaulting a minor. After his release from prison in 2012, D came to live in New York. But he never registered there as a sex offender. D was convicted for failing to register. D argued that Congress unconstitutionally delegated legislative power when it authorized the Attorney General to “specify the applicability” of SORNA’s registration requirements to pre-Act offenders. The District Court and the Court of Appeals affirmed his conviction. The Supreme Court granted certiorari.