The Federalist Society weighs in...On Spygate

“To conduct a wiretap without statutory authorization, either in wartime or peacetime, is a crime, punishable by up to five years in prison.”

The statute reads: “Notwithstanding any other law, the President, through the Attorney General, may authorize electronic surveillance without a court order under this title to acquire foreign intelligence information for a period not to exceed fifteen calendar days following a declaration of war by the Congress.”

Yes, I believe that the president has constitutional powers to order warrantless wartime surveillance. For example, intercepting enemy communications on the battlefield is clearly an incident of the president’s war power. But warrantless wiretapping of Americans inside the United States who may have nothing to do with Al Qaeda does not qualify as an incidental wartime authority. The president’s war powers are broad, but not “plenary” as your question implies. Indeed, Congress, not the president, is constitutionally authorized to suspend habeas corpus, “define and punish … Offenses against the Law of Nations,” “declare War,” “raise and support
Armies,” “provide and maintain a Navy,” and “make Rules for the Government and Regulation of the land and naval forces.”

"…Even under Youngstown’s second category (congressional silence), the president might have inherent authority pursuant to the Commander-in-Chief Clause to interpret the “reasonableness” standard of the Fourth Amendment in a manner that would sanction certain warrantless searches. But the NSA program does not fit in Youngstown’s second category. It belongs in the third category, in which the president has acted in the face of an express statutory prohibition. In my view, he has overreached."