And in doing so Congress would run up against separation of powers issues, because in our system, it's not really Congress's place to dictate to the President h

And in doing so Congress would run up against separation of powers issues, because in our system, it's not really Congress's place to dictate to the President how he carries out foreign security activities. I agree with you completely, but when the political will is there, Congress can dive head first into separation of powers fights. Look at the War Powers Resolution. It's almost certainly unconstitutional in a strict sense, or at least extra-constitutional. But the Supreme Court will likely never touch it, and Presidents take its requirements seriously. One potential avenue for limiting foreign intelligence gathering short of an amendment would be ratifying a treaty to that effect. But that seems as unlikely as any other route, since, as has been pointed out a few times, most Americans care not a lick about foreign SIGINT, and to the extent they do would like it to be as effective as possible.