John Yoo, Bush’s chief legal advisor:

"We are used to a peacetime system in which Congress enacts the laws, the president enforces them, and the courts interpret them. In wartime, the gravity shifts to the executive branch.”

This is simply flat-out entirely 100% untrue.

Our "system" is set out in the Constitution, and it’s the same "system" regardless of whether we are at peace and at war.  It’s not like we have a "peacetime" Constitution, and a "wartime" Constitution.

Glenn Greenwald gets to the heart of the matter:

The Constitution is actually pretty clear on that score. Article I says "All legislative Powers herein granted shall be vested in a Congress of the United States" — Article II says the President "shall take Care that the Laws be faithfully executed" — Article III says "the judicial Power of the United States, shall be vested in one supreme Court, and in . . . inferior Courts." That arrangement isn’t really a side detail or something that shifts based on circumstance. It’s pretty fundamental to the whole system. In fact, if you change that formula, it isn’t really the American system of government anymore.