It is a logical impossibility for any treaty to supersede the Constitution. For the same reason it’s a logical impossibility for any Act of Congress to do so.
The US Constitution allows no such thing. The language of Article VI is commonly misinterpreted that way by ignoramuses, but the historical record regarding the original intent is emphatically clear that the Constitution itself is the supreme law of the US, and no lesser law or treaty has the power to circumvent it. Which is in fact the originally intended semantics of the language in Article VI (read very carefully):
“****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.”
The Constitution also states that the only way to change it is to officially amend it—and treaties are not, de jure, amendments. ... Read More
Unless it is officially amended, treaties are subject to the same limitation as any Act of Congress: They must a) not violate the restrictions the Constitution places on government action, and b) be justified by an explicit enumerated power granted to the government by the Constitution. The power to make treaties does not grant any power to violate the Constitution itself, any more than the power to make laws does. Laws can be declared Unconstitutional in spite of the language of Article VI—and so can treaties, for the same reasons.