If United States is signatory of an treaty signed with another state which is still valid, what is position of that treaty which regulates something (for example giving citizen of state which is signatory of treaty some rights in US) according to valid laws of United States?
The constitution has the "Treaty Clause" (article II, section 2) which states that the president "shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur". There is no legal concept of "signing" a treaty in the US, and only ratification counts. It is unclear what limits there are to enforcement of treaties in lieu of statutory enactment. Medellín v. Texas held that
While a treaty may constitute an international commitment, it is not binding domestic law unless Congress has enacted statutes implementing it or the treaty itself conveys an intention that it be “self-executing” and is ratified on that basis
This was a reversal of prior trends going back to Ware v. Hylton based on the Supremacy Clause, that
all Treaties … 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
But Medellín doesn't mean "never": you have to "parse a treaty's text to determine if it is self-executing", which is a different ball of wax.
What is internationally considered a "treaty" may be considered several different things in US legal terminology, depending on how it was enacted in the US:
- A "treaty" (under the meaning of the Treaty Clause of the Constitution), ratified by two thirds of the senate. Such a ratified treaty has a similar position under US law as a regular federal Act of Congress. Like an Act of Congress, a "treaty" can be modified or repealed (for the purposes of US law) simply by passing a subsequent Act of Congress that modifies or repeals it, according to the Supreme Court ruling in the Head Money Cases. Also like an Act of Congress, a "treaty" is inferior to the US Constitution and any provision that conflicts with the Constitution is null and void (for the purposes of US law), according to the Supreme Court ruling in Reid v. Covert. In one sense, however, a treaty may be somewhat more powerful than Acts of Congress, because according to the Supreme Court ruling in Missouri v. Holland, a treaty can act in areas that Congress doesn't have the power to act, and which ordinarily belongs to the states, although there is question about the validity of this ruling today.
- A "congressional-executive agreement", which is an executive agreement concluded by the President, and then the parts requiring legislative changes are passed through Congress as regular legislation. Since it is passed as regular legislation, it has exactly the same position as regular legislation.
- A "sole executive agreement", which is an executive agreement concluded by the President, which does not involve any action by Congress. It has the same position in US law as an executive order or executive action by the President, and hence can only act in areas where the President already has the legal authority to act alone.