I'm pleased to say that my latest article has just been published: Cross-Enforcement of the Fourth Amendment, 132 Harv. L. Rev. 471 (2018). Here's the abstract:
This Article considers whether government agents can conduct searches or seizures to enforce a different government's law. For example, can federal officers make stops based on state traffic violations? Can state police search for evidence of federal immigration crimes? Lower courts are deeply divided on the answers. The Supreme Court's decisions offer little useful guidance because they rest on doctrinal assumptions that the Court has since squarely rejected. The answer to a fundamental question of Fourth Amendment law — who can enforce what law — is remarkably unclear.
After surveying current law and constitutional history, the Article offers a normative proposal to answer this question. Each government should have the power to control who can enforce its criminal laws. Only searches and seizures by those authorized to act as agents of a sovereign trigger the government interests that justify reasonableness balancing based on those interests. The difficult question is identifying authorization: questions of constitutional structure suggest different defaults for enforcement of federal and state law. Outside the Fourth Amendment, governments can enact statutes that limit how their own officers enforce other laws. The scope of federal power to limit federal enforcement of state law by statute should be broader, however, than the scope of state power to limit state enforcement of federal law.
There's a Volokh-Conspiracy-related angle to this article, although it's pretty obscure. Long-time dedicated readers may remember that back in 2008, before the oral argument in Virginia v. Moore, I became super-interested in the constitutional status of United States v. Di Re. Was that case applying the Fourth Amendment, or was it based in the supervisory power? I was pretty sure it was the former, although others disagreed. Almost a decade later, when I started researching this article, I was amazed to see that the Supreme Court's answer to the questions I was studying seemed to hinge on determining the constitutional status of United States v. Di Re. Years later, I think I finally answered the riddle, see pages 508-514. I guess everything ends up being relevant somehow.