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.
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* Frances R. and John J. Duggan Distinguished Professor, University of Southern California Gould School of Law. Thanks to Dan Klerman, Will Baude, Barry Friedman, Stephen Sachs, Wesley Oliver, Scott Altman, Jonathan Barnett, Scott Bice, Alexander Capron, David Cruz, Gregory Keating, Nomi Stolzenberg, Rebecca Lonergan, Thomas Davies, Lauryn Gouldin, Sara Sun Beale, Curtis Bradley, Nita Farahany, Guy-Uriel Charles, Walter Dellinger, and participants in the Duke Law School Faculty Workshop and the AALS Criminal Justice Section Midyear Meeting for helpful conversations and comments on a prior draft. I thank Zachary Tyree for excellent research assistance.