Can Congress Invent New Offenses Against the Law of Nations?

Lawfare’s Alex Loomis has an excellent paper on SSRN that might interest Lawfare readers: The Power to Define Offences against the Law of Nations. From the abstract:

Congress has the power to “define and punish . . . Offences against the Law of Nations.” Everyone agrees this clause empowers Congress to punish universally recognized offences under international law, piracy being the clearest example. But Congress has the power to “define” offences against the law of nations too. Surely punishing an offence presupposes defining it. So what does “define” add?

This paper provides an answer. The Constitution’s text and structure, early constitutional history, and modern foreign relations doctrine all suggest Congress has the power to define offences against the law of nations that preexisting international law does not proscribe. Congress may pass laws prohibiting private conduct that violates international law, as well as any private conduct that, while itself not illegal under international law, the United States has a duty to punish. Any ambiguity about the United States’s obligation to punish the conduct in question does not restrict Congress’s power to define and punish. Congress likely even has the power to create new offences against the law of nations in order to foster changes in customary international law.

The paper has obvious relevance to the pending en banc proceeding in Bahlul in the D.C. Circuit