Supremacy Clause

The Supremacy Clause appears in Article VI, Clause 2 of the U.S. Constitution. It declares that the Constitution, federal statutes "made in Pursuance thereof," and treaties made under U.S. authority constitute "the supreme Law of the Land," binding judges in every state notwithstanding any contrary state constitution or law.

The clause is the textual foundation for the doctrine of federal preemption, under which valid federal law displaces conflicting state law. Courts generally recognize several preemption categories: express preemption (where Congress states its intent in statute), conflict preemption (where compliance with both is impossible or state law obstructs federal objectives), and field preemption (where federal regulation is so pervasive it occupies the area).

Chief Justice John Marshall's opinion in McCulloch v. Maryland (1819) relied on the clause to strike down Maryland's tax on the Second Bank of the United States, reasoning that states cannot tax or impair valid federal instrumentalities. In Gibbons v. Ogden (1824), the Court used it to invalidate a New York steamboat monopoly that conflicted with a federal coasting license. More recent applications include Arizona v. United States (2012), where most provisions of Arizona's immigration enforcement law (S.B. 1070) were held preempted by federal immigration law.

For international-relations researchers, the clause is particularly relevant to treaty implementation. It places ratified treaties on par with federal statutes as supreme law, but U.S. courts distinguish between self-executing treaties (directly enforceable in domestic courts) and non-self-executing treaties (requiring implementing legislation). In Medellín v. Texas (2008), the Supreme Court held that an International Court of Justice judgment under the Vienna Convention on Consular Relations was not directly enforceable against Texas without congressional action, narrowing the practical reach of the clause over treaty obligations.

The clause does not subordinate the Constitution to treaties; Reid v. Covert (1957) confirmed that treaties cannot override constitutional protections.