Never in the nation’s history has the scope and meaning of Congress’s power to “define and punish . . . Offences against the Law of Nations” mattered as much. The once-obscure power has in recent years been exercised in broad and controversial ways, ranging from the Alien Tort Statute (ATS) to military commission trials in Guantanamo Bay. Yet it has not yet been recognized that these issues both involve the Offenses Clause and indeed raise common constitutional questions. First, can Congress “define” offenses that clearly already exist in international law, or does it have discretion to codify debatable or even nonexistent international law norms? Second, what happens to this discretion when it delegates the power to a coordinate branch?
This Article shows that the Offenses Clause allows Congress only to “define”—to specify the elements and incidents of—offenses already created by customary international law. It does not allow Congress to create entirely new offenses independent of preexisting international law. At the same time, the Framers understood international law to be vague and intertwined with foreign policy considerations. Thus, courts reviewing congressional definitions should give them considerable deference. Moreover, whatever discretion Congress has in defining offenses disappears when it broadly delegates that power to another branch, as it has in the ATS. The Supreme Court suggested a similar standard for ATS causes of action in Sosa v. Alvarez-Machain. Appreciating the role of delegation in the ATS shows that the limits on offenses that can be litigated under the statute have a constitutional dimension.
The Article develops the original understanding of the Offenses Clause—particularly important given the lack of any judicial decisions on it in the nation’s first century. It draws on previously unexplored sources, such as early cases about the meaning of the “define” power in the cognate context of “piracy and felonies,” legislation by early Congresses, and discussions by Framers like Madison and others.