Article VI, the Supremacy Clause of the Constitution, declares:
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; . . .
There is nothing in this language which intimates that treaties and laws enacted pursuant to them do not have to comply with the provisions of the Constitution. Nor is there anything in the debates which accompanied the drafting and ratification of the Constitution which even suggests such a result. These debates, as well as the history that surrounds the adoption of the treaty provision in Article VI, make it clear that the reason treaties were not limited to those made in "pursuance" of the Constitution was so that agreements made by the United States under the Articles of Confederation, including the important peace treaties which concluded the Revolutionary [p17] War, would remain in effect. [n31]
It would be manifestly contrary to the objectives of those who created the Constitution, as well as those who were responsible for the Bill of Rights -- let alone alien to our entire constitutional history and tradition -- to construe Article VI as permitting the United States to exercise power under an international agreement without observing constitutional prohibitions. [n32] In effect, such construction would permit amendment of that document in a manner not sanctioned by Article V. The prohibitions of the Constitution were designed to apply to all branches of the National Government, and they cannot be nullified by the Executive or by the Executive and the Senate combined.
There is nothing new or unique about what we say here. This Court has regularly and uniformly recognized the supremacy of the Constitution over a treaty. [n33] For example, in Geofroy v. Riggs, 133 U.S. 258, 267, it declared: