Time for a civics lesson and I'll attempt a little Q & A in my half-assed way of having a Socratic dialogue:
Q: Are treaties law?
A: Yes. Article VI Clause 2 of the US Constitution reads as follows:
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. [my emphasis]
Q: How do treaties become law?
A: They are signed by the president and must be submitted to the Senate and a 2/3 vote of the Senators present is needed for approval or ratification.
Q: Is the Convention Against Torture (CAT) a treaty?
Q: Did the president sign it?
A: Yes, President Reagan signed it on April 11, 1988 and the senate ratified it on October 21, 1994.
Q: Why did it take so long to be ratified?
A: Because on signing the treaty the US made a list of several reservations including this one: "That the United States declares that the provisions of articles 1 through 16 of the Convention are not self-executing."
Q: What did that mean?
A: That meant that specific laws had to be passed and signed into law which essentially made torture a crime under United States Law and provided for jurisdiction by the US regardless of where torture is committed provided either the "the alleged offender is a national of the United States; or the alleged offender is present in the United States, irrespective of the nationality of the victim or alleged offender." This law is commonly referred to as either the CAT implementing legislation or the Torture Statute.
Q: So the terms of the Convention Against Torture is the law of the land in the United States, right?
A: Yes it is, with the exception of the few reservations the US made.
Q: Aren't there exceptions when torture can be justified?
A: No, Article 2 Paragraph 2 states "No exceptional circumstances whatsoever, whether a state of war or a threat of war, internal political instability or any other public emergency, may be invoked as a justification of torture."
Q: Did the United States have a reservation regarding this section?
Q: What is the role of the Executive Branch of the Federal Government?
A: The role of the Executive Branch is to enforce the laws.
Q: Who is in charge of the Executive Branch?
A: The President of the United States.
Q: So would it be fair to say that the president is the chief law enforcement officer of the United States?
A: Article II, Section 3 of the US Constitution states that among the president's duties "he shall take Care that the Laws be faithfully executed." So although it is not specifically spelled out in the Constitution that the president is the chief law enforcement officer of the United States, given that he is in charge of the Executive Branch and the Executive Branch enforces the laws and among his duties is to take care that the laws are faithfully executed, your answer is essentially correct.
Q: So given his role as chief law enforcement officer and given the fact that the Convention Against Torture is the law of the land and given the fact that the Convention Against Torture provides for ""No exceptional circumstances whatsoever, whether a state of war or a threat of war, internal political instability or any other public emergency, may be invoked as a justification of torture," why would the president's legal advisers say "The president, despite domestic and international laws constraining the use of torture, has the authority as commander in chief to approve almost any physical or psychological actions during interrogation, up to and including torture?"
A: I cannot possibly explain why.
As Michael Froomkin said:
"And just imagine what those guys will do if they don’t have to worry about re-election."