A couple of apologists for Bush’s warrantless wiretapping wax indignant in an op-ed in today’s New York Times. Yet when it comes right down to it, former DOJ lawyers David B. Rivkin and Lee A. Casey base everything on the following assertion:

Even if Congress had intended to restrict the president’s ability to obtain intelligence in such circumstances, it could not have constitutionally done so. The Constitution designates the president as commander in chief, and Congress can no more direct his exercise of that authority than he can direct Congress in the execution of its constitutional duties.

But this is nonsense. The US Constitution uses the term “commander in chief” only once:

Section 2
The President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States

This merely identifies the role of the President in the military command structure of the Army, Navy and Militia. It confers absolutely no powers with respect to any other agencies of government, nor does it specify that this authority is not subject to constitutional and legislative control. Indeed the Supreme Court ruled on this in 1952. The failure of Bush apologists like Rivkin and Casey to even consider this point is significant, as is their reluctance to come right out and claim that FISA is unconstitutional.
(This is a pretty useful background article.)
UPDATE: Marshall Grossman expresses it much better than I did.