This Constitutioon, 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.
In interpreting this article of the Constitution, here is what the Supreme Court said when citizens of Switzerland, pursuant to a treaty between the United States and Switzerland, were trying to remove certain monies from the possession of the state of Virginia:
If doubts could exist before the adoption of the present national government, they must be entirely removed by the sixth article of the Constitution, which provides that '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 law of any State to the contrary notwithstanding ... A treaty cannot be the supreme law of the land, that is, of all the United States, if any act of a State legislature can stand in its way. . . It must always be borne in mind that the Constitution, laws, and treaties of the United States are as much a part of the law of every State as its own local laws and Constitution. This is a fundamental principle in our system of complex national polity Hauenstein v. Lynham, 100 U.S. 483 (1880).