The power to protect the nation, said Alexander Hamilton in the Federalist, "ought to exist without limitation," because "it is impossible to foresee or define the extent and variety of national exigencies, or the correspondent extent & variety of the means which may be necessary to satisfy them." To limit the president's constitutional power to protect the nation from foreign threats is simply foolhardy. Hamilton observed that "decision, activity, secrecy, and dispatch will generally characterize the proceedings of one man, in a much more eminent degree, than the proceedings of any greater number." "Energy in the executive," he reiterated, "is essential to the protection of the community against foreign attacks."

My suspicion is that if they had said "Hey, we were looking everywhere but if it didn't lead to actual terror cells we simply forgot it" instead of "Oh, were only doing it for national security but if we find evidence of people doing other crimes we're referring it to the regular prosecutors" it probably would have been OK. Also, it strikes me as valid as an exception for about six months until you can get up to speed. After five or six years, your just taking advantage ...