[BluffTHIS!]

bobman, I think you are right in your analysis. I remembered the court action over the line item veto because I remember members of congress challenging it. Their suit was thrown out due to lack of standing. I googled and found the following regarding standing to bring suit:

Traditional standing doctrine requires that a plaintiff have "personal injury fairly traceable to the defendant's allegedly unlawful conduct and likely to be redressed by the requested relief." Moreover, the personal injury must be "concrete and particularized." Congress cannot grant standing to someone who does not satisfy the Constitutional standing requirements by purporting to authorize them to bring suit.

The line item veto was ultimately struck down when some hospitals affected by a line item veto of certain medicare spending brought suit. Thus it would seem that the only way this thing might be tested in court is for someone who is the subject of a warrantless wiretap to bring suit. But of course it would be almost impossible to prove it had happened since the government will say the matter is classified. And any such subject is obviously going to have to be totally innocent of any suspected wrong-doing or he is not going to be bringing such action.

And just as obviously, no federal prosecutor is going to bring action against the president on this matter, even if he is thought to have violated the law. So the only way for congress to do anything regarding past such actions, would indeed be to attempt to bring impeachment proceedings, which of course isn't going to fly in a repub congress, or even with repubs as a significant minority in the senate.

The only thing congress can do it looks like, is regarding the future by ammending the FISA to make it more clear, which the repubs won't go for either.