You are right it is legal...take a course on intelligence oversight.
These lawyer talking heads don't know what they are talking about, the President's authorities and don't want to acknowledge that the President retains war powers authorities and is the lead for foreign intelligence.
...NO PRESIDENT has accepted the "War Powers Act" as binding; Congressional FISA legislation is comformed with for reasonableness reasons-- it does not impede national security and protects rights,but the President is not bound by Congress on that either...for those who keep whining about FISA-- the FISA court of review admitted the President's "inherent" authorities to conduct "warrantless searches;" it is done for foreign intelligence not for personal or political gain and Congress has been informed...
Do not forget Article 1 Section 9 in the Constitution...Bush can suspend habeous corpus and throw the NYT editorial staff and journalists in jail for violating national secrets and if he can do that he can certainly use NSA for domestic surveillance tied to foreign intelligence.
...that also means he can keep those little 'sh..heads' in GITMO as long as wants irrespective of what any court says if he needs to play that card...
Article I relates to Congressional powers, not executive powers.
Ex parte Merryman, 17 F. Cas. 144 (1861)
Ex Parte Milligan, 71 U.S. 1 (1866)
BOTH cases found Lincoln's suspensions of habeas corpus to be unconstitutional.
Not that ALL unilateral executive suspensions of habeas corpus would be, but those were.
See today's news Man who sold U.S. secrets gets 12 years in prison