In a recently declassified March 2003 memo to the Pentagon's top lawyer, former Deputy Assistant Attorney General John Yoo lays out "the legal standards governing military interrogations of alien unlawful combatants held outside the United States." Yoo reiterates his notoriously demanding definition of torture, which requires suffering "equivalent to the pain that would be associated with serious physical injury so severe that death, organ failure, or permanent damage resulting in a loss of significant body function will likely result." But this generous understanding of how far the Pentagon can go without violating the statutory prohibition of torture is not really necessary, since Yoo asserts that Congress has no authority under the Constitution to ban the torture of military prisoners in the first place:

In wartime, it is for the President alone to decide what methods to use to best prevail against the enemy....One of the core functions of the Commander in Chief is that of capturing, detaining, and interrogating members of the enemy....The President enjoys complete discretion in the exercise of his Commander-in-Chief authority in conducting operations against hostile forces....Congress cannot interfere with the President's exercise of his authority as Commander in Chief to control the conduct of operations during a war....Any construction of criminal laws that regulated the President's authority as Commander in Chief to determine the interrogation and treatment of enemy combatants would raise serious constitutional questions whether Congress had intruded on the President's constitutional authority....Congress may no more regulate the President's ability to detain and interrogate enemy combatants than it may regulate his ability to direct troop movements on the battlefield.

According to Yoo, then, no statutory restriction on the Pentagon's treatment of its prisoners, presumably including "enemy combatants" unilaterally identified by the president and arrested on U.S. soil, could be legally binding, because it would unconstitutionally impinge on the president's powers as commander in chief. Never mind that the Constitution gives Congress the authority not only to declare war but "to make rules concerning captures on land and water," "to make rules for the government and regulation of the land and naval forces," and to suspend the habeas corpus privilege "in cases of rebellion or invasion," all of which seem to imply that the legislative branch has some say regarding the handling of military prisoners.

In Yoo's view, the president's constitutional powers are so broad that the Constitution itself cannot restrain them. As the ACLU notes, a footnote on page 8 of the memo refers to a still-classified October 2001 document in which the Justice Department's Office of Legal Counsel "concluded that the Fourth Amendment had no application to domestic military operations." That position provides a legal rationale not just for the National Security Agency's warrantless surveillance of international communications involving people in the U.S. but for monitoring of purely domestic phone calls and email as well. Indeed, it justifies warrantless domestic searches and seizures of any kind, provided they are carried out by a branch of the Defense Department that asserts a connection to terrorism or some other national security threat. 

The Justice Department has repudiated both Yoo's March 2003 memo and his August 2002 memo addressing torture. But it's not clear to what extent it still concurs with Yoo's sweeping view of executive power. During his confirmation hearings, Attorney General Michael Mukasey conceded that the president is bound to obey statutes regulating the treatment of military prisoners. But he dodged the question of whether Congress has the authority to regulate domestic surveillance conducted in the name of national security. No one thought to ask him whether the president is bound to obey the Fourth Amendment, presumably because no one imagined that even this administration would claim otherwise. Now we know better.

The full text of the March 2003 memo is available from the ACLU here.