The Supremacy Clause

The Text

This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the contrary notwithstanding.

What It Says

The Constitution and federal laws made under it are the highest law, binding on state judges. The qualifier matters: only laws made in pursuance of the Constitution qualify.

What It Protects Against

Two opposite failures. Without it, states could nullify federal law at will. Read without the in pursuance thereof qualifier, it becomes a claim that whatever the federal government enacts is automatically supreme.

Sourced to a ratification-era document. See Contemporaneous Defense below.

Problem Addressed

Under the Articles of Confederation, federal measures depended on state cooperation and were routinely ignored, leaving the union unable to enforce its own treaties.

Contemporaneous Defense

Federalist No. 33 addressed the clause directly, arguing that a law not made in pursuance of the Constitution is not law at all but a usurpation, and that the qualifying phrase is the whole of the limitation.