If you're interested in the Administration position with respect to this, here's the excerpt from the DOJ white paper
Even if there were ambiguity about whether FISA, read together with the AUMF, permits the President to authorize the NSA activities, the canon of constitutional avoidance requires reading these statutes in harmony to overcome any restrictions in FISA and Title III, at least as they might otherwise apply to the congressionally authorized armed conflict with al Qaeda. Indeed, were FISA and Title III interpreted to impede the President’s ability to use the traditional tool of electronic surveillance to detect and prevent future attacks by a declared enemy that has already struck at the homeland and is engaged in ongoing operations against the United States, the constitutionality of FISA, as applied to that situation, would be called into very serious doubt. In fact, if this difficult constitutional question had to be addressed, FISA would be unconstitutional as applied to this narrow context. Importantly, the FISA Court of Review itself recognized just three years ago that the President retains constitutional authority to conduct foreign surveillance apart from the FISA framework, and the President is certainly entitled, at a minimum, to rely on that judicial interpretation of the Constitution and FISA.