Professor Jack Balkin offers initial thoughts on the Military Commissions Act:
First, the MCA puts the President in an interesting position: the U.S. is still bound by Geneva, but there is no way for individuals to enforce violations of Geneva (except that grave breaches of Common Article 3 can still be prosecuted under the War Crimes Statute). However, Geneva's status as the law of the land (under Article VI) was not altered by the MCA. The United States has not withdrawn from the Geneva Conventions, and this fact was quite important to selling the bill to the public. So if the President orders procedures that are inconsistent with Geneva, he is still acting contrary to law even though there may be no way for an individual to enforce the law directly.
Second, the President remains bound by the prohibitions against cruel, inhuman and degrading treatment found in the McCain Amendment, and the substantive tests of the Fifth, Fourteenth and Eighth Amendments, whether the conduct occurs in the United States our outside of it. Indeed, the MCA reaffirms these substantive standards and makes them applicable throughout the world. If the President violates these standards, or directs others to do so, he violates the law. That means if the President interprets these standards narrowly and tendentiously to permit certain interrogation practices, he also violates the law. There is just no judicial remedy for the violation.
Let me repeat what I have just said: The MCA continues to recognize that certain conduct is illegal, but attempts to eliminate all judicial remedies for such violations. That means that if the President violates the MCA, he still fails to take care that the laws be faithfully executed, which is his constitutional duty under Article 2, section 3 of the Constitution. (And in case you are wondering, he might well be guilty of a high crime and misdemeanor, but don't hold your breath.)