They just do what they want and say anything to justify it:

U.S. Constition, Article I, Section 8: (selections, emp add):

The Congress shall have power to

make rules concerning captures on land and water;

make rules for the government and regulation of the land and naval forces;

From the Post's report on Cheney: (emp add)

The vice president's lawyer advocated what was considered the memo's most radical claim:     that the president may authorize any interrogation method, even if it crosses the line into torture. U.S. and treaty laws forbidding any person to "commit torture," that passage stated, "do not apply" to the commander in chief, because

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."