A doctrine asserting that individual states may refuse to enforce or treat as void federal statutes they deem unconstitutional, claiming a state-level check on national legislation. Invoked most famously by South Carolina in the 1832 crisis under John C. Calhoun and justified by appeals to the Tenth Amendment, it directly conflicted with the Supremacy Clause (Article VI) and judicial review (Marbury v. Madison), shaping enduring federal–state power struggles.