Eric Umansky finds Marty Lederman explaining what is going on:
Marty Lederman : The rhetoric of "inherent" presidential power is obscuring what's at issue here. Perhaps he would have had the power to authorize some of this conduct (hard to tell how much -- we don't know enough about it) had federal law never addressed the issue. But this is not a case in which the President acted with Congress's consent, where his authority is at its apex; nor where he acted unilaterally, in the face of congressional silence. Instead, this is a case in which the American public had a comprehensive, contentious, and long public debate, borne of a serious history of government abuse, and our elected representatives -- both Executive and Legislature -- regulated this subject matter in great detail (going so far as to enact a specific exigency-in-war provision), and flatly prohibited the conduct in question -- a consensus resolution that all three branches and the public came to rely upon and take for granted as common ground for almost 30 years.
Instead of moving to change that, the Administration simply decided to circumvent what the Legislature had already decided to do. And they did so without even telling the legislature about it, let alone the public. Indeed, they kept acting as if all was just as it had been for 25+ years. And then when they were found out, their explanation was that the legislature had, unknowingly, effected a radical change in the law when they voted to allow the use of force against Al Qaeda -- i.e, they blamed it on Congress, which is, not surprisingly, a form of argument ("we know better than you what you intended") that seems to have really set off many folks on the Hill (and on the FISA court, whose judges were also played for dupes).
This is, in other words, a classic Youngstown Category III case of an imperial Executive, not acting unilaterally, as Lincoln did, or in conformity with legislative will (as Lincoln claimed to be doing -- he agreed to abide by whatever limitations the Congress enacted), but instead in direct violation of the decisions that were reached in the democratic process. I hope that would be, and will be viewed as, deeply problematic, regardless of one's views on the merits of whether we ought to have a system of data mining...