Although the Constitution grants Congress extensive legislative powers, it vests Congress with explicit authority to enact criminal law in only three places. Moreover, the authority it places in the hands of Congress includes an implementing power, that is, the authority to enact laws necessary and proper to the implementation of those other powers—authority that by implication includes the authority to enact reasonably related criminal laws. Whether understood as contextual, or structural, or implicit in the Tenth Amendment, they are the limitations of federalism, the limitations that flow from the fact the Constitution emerged as a compact between the sovereign it created and the sovereigns that created it. What follows is a discussion of selected recent cases that illustrate the scope and boundaries of Congress's power to enact criminal laws under the Constitution's necessary and proper, commerce, high seas, law of nations, spending, and military clauses. The Supreme Court has granted certiorari in Bond and Kebodeaux . The Ninth Circuit, in United States v. Elk Shoulder , applied the same considerations and came to opposite conclusions in the case of a federal sex offender still under supervised release. The Fifth Circuit disagreed. Its criminal penalties only apply with respect to state sex offenders who travel in interstate commerce or to federal sex offenders. The Third Circuit Court of Appeals initially held that Mrs. When the case returned to the Third Circuit for a decision on the merits, the court was faced with the question of the extent to which principles of federalism limit congressional authority under the Necessary and Proper Clause to implement a United States treaty. Moreover, the Court held in Lopez that the Commerce Clause did not empower Congress to enact statutes that outlawed possession of a firearm in a school yard and in Morrison that it does not permit creation of a federal cause of action for the victims of violent, gender-based animus. Chief Justice Roberts, joined by Justices Breyer and Kagan, observed that the power to regulate commerce does not include the power to require individuals to engage in commerce. However, the scope of the Commerce Clause defines the scope of congressional authority to enact implementing criminal legislation. United States v. Kebodeaux

Having concluded that application of SORNA in the case before it exceeded Congress's Necessary and Proper powers, the Fifth Circuit in Kebodeaux also rejected the suggestion that SORNA, as applied, might be considered a valid exercise of Congress's Commerce Clause powers under the "channels of commerce," the "instrumentalities of commerce," or the "substantial effect on commerce" prong of the Clause. A dissenting member of the panel objected that the Foreign Commerce Clause should not be read to permit Congress to regulate all commercial activities once an individual has engaged in international travel. Article I, Section 8, Clause 10

The Congress shall have Power ... To define and punish Piracies and Felonies committed on the high Seas, and Offenses against the Law of Nations. It then decided that an offense must be contrary to customary international law in order to constitute an offense against the law of nations. Early on, the lower federal appellate courts concluded that Congress's power "to define and punish Piracies and Felonies committed on the High Seas, and Offences against the Law of Nations" vested it with authority to enact MDLEA. Its sole remaining concern was any due process limitation on Congress's ability to reach foreign nationals traveling outside U.S. territorial waters. The Supreme Court has said in the past that Congress's exercise of the Spending Clause is subject to certain limitations: "[F]irst[,] ... the exercise of the spending power must be in pursuit of 'the general welfare.' Congress may employ the power of the purse to encourage the states to participate in a federal program; it may not use it to compel them to do so.
The powers of Congress begin and end with the Constitution. The Constitution vests Congress with explicit authority to enact criminal laws relating to counterfeiting, piracy, crimes on the high seas, offenses against the law of nations, and treason. It grants Congress other broad powers, such as the power to regulate interstate commerce. The Constitution's Necessary and Proper Clause allows Congress to enact criminal laws when reasonably related to the regulation of commerce or to one of the other constitutionally enumerated powers. The Constitution also imposes limits on the powers of Congress, however. It places those limits in the terms it uses in its grants of authority, in explicit prohibitions, and in the Tenth Amendment reminder of the restrictions implicit in the federal union. Recently, the Supreme Court and the lower federal appellate courts have supplied several examples of the scope and limits of congressional authority.
In the case of the Commerce Clause, seven Justices of the Supreme Court endorsed separate opinions in National Federation explaining that the power to regulate interstate commerce does not include the power to require participation in commerce. The Fifth Circuit held in Kebodeaux that the Commerce Clause does not embody the power to outlaw purely intrastate movement with only an attenuated nexus to commercial activity. As for foreign commerce, the circuits disagree on whether Congress's regulatory authority is subject to the same constraints that apply to its powers over domestic commerce. The Ninth Circuit (Clark) believes it is not. The Third Circuit (Pendleton) disagrees. (The Violence Against Women Reauthorization Act, P.L. 113-4 (S. 47), eliminates the need to prove a foreign commerce element in the law that gave rise to the circuit split.)
In the realm of the Necessary and Proper Clause, the Eleventh Circuit in Belfast observed that Congress may pass criminal legislation in order to implement a treaty obligation, and the Third Circuit in Bond held that it may do so without regard to federalism concerns. Moreover, the Ninth Circuit Court of Appeals concluded in Elk Shoulder that Congress may outlaw the unregistered movement within a state of a federally convicted sex offender who is on supervised release. The Fifth Circuit held in Kebodeaux, however, that the Clause does not permit enactment of a statute that outlaws such movement after the offender has been fully discharged. Although they did not join in a single opinion, seven Justices in National Federation concluded that Congress's power under the Spending Clause may not be used to compel the states to accept expansion of a federal regulatory regime or to face draconian economic consequences. The case did not involve criminal penalties, but a limit on Congress's Spending Clause power is a limit on its authority to enact implementing necessary and proper criminal legislation.
Article I, Section 8, clause 10 grants Congress the power "to define and punish Piracies and Felonies committed on the high Seas, and Offenses against the Law of Nations." Federal appellate courts have looked to customary international law for explanations of the power over offenses against the law of nations (Bellaizac-Hurtado) and piracy (Dire). The High Seas cases (Saac and Ibarguen-Mosquera) continue to acknowledge congressional authority to outlaw drug trafficking in international waters subject only to an elusive due process limitation. The Constitution's Military Clauses permit Congress to criminalize overseas assaults by Defense Department foreign contractors (Brehm), but do not permit it to punish an individual's conduct based solely on his status as a former member of the Armed Forces even when supplemented by the Necessary and Proper Clause (Kebodeaux).