The public can't do much because it has given too much power to intelligence agencies already. Today, the left and right almost unanimously hate intelligence agencies, but their power is entrenched.
Case in point: the Constitution is irrelevant to intelligence agencies. They genuinely believe they can operate completely outside of it and face no punishment, so they frequently do. What can an American citizen do at that point?
And who even wants to speak out against an intelligence agency if it'll put you on a list?