The virtually-always-worth-reading Glenn Greenwald at Unclaimed Territory seems to have broken this story. Be sure to read his post, but the executive summary goes something like: Yesterday the Administration trotted out Michael Hayden, the former head of the NSA, to explain that the probable cause requirement for obtaining FISA warrants impaired the security of the U.S. (hence necessitating the creation of the NSA program, which allowed wiretaps on the basis of the lower standard of reasonable suspicion). Yet (Greenwald has now revealed), in 2002 the same Administration opposed an amendment offered by Senator Mike DeWine that would have lowered the required showing for FISA warrants from probable cause to reasonable suspicion, on grounds that the proposed change was both unnecessary to the national defense and probably unconstitutional to boot. And the Administration took this position on the amendment several months after initiating the NSA program, which needless to say, was a far more radical and legally questionable change in the FISA procedures than the DeWine amendment insofar as it completely eliminated any judicial oversight of the reasonable suspicion requirement. But read the whole story, it's pretty convincing: Unclaimed Territory - by Glenn Greenwald: The Administration's new FISA defense is factually false.
Update: By the way, those looking for a short, convincing statement listing the arguments against the legality of the NSA surveillance program (signed by 14 prominent law professors) can find it here, among many other places. Relatedly, on the same blog, one of the signers of the letter (U. of Chicago Law Professor Geoffrey Stone) has an excellent post (and a useful one, because bile- and cant-free -- some people don't seem to like bile and cant with their political arguments) on why Judge Alito should not be confirmed by the Senate, here.
Update #2: And for those who just can't get enough political irony, see this post at Balkinization as well --