Many people are speculating that the illegal wire tap program included a program to spy on political figures, .... enemies as well as friends. Let me be the first to say that it wouldn't surprise me to find it's true.
But.
If I had to guess (like everyone else at this point), I'd say that this is not why the program was developed and FISA bypassed. I think it's simply a matter of thousands, perhaps millions, of Americans having been tapped in a data mining operation. With these numbers, it's simply unfeasible to get warrants. And to pursue a change in legislation through Congress would have blown the program due to leaks. Not to mention that Congress may not have agreed to such a widespread violation of civil rights.
Like I said, I wouldn't be at all surprised to be found wrong. Either way it's impeachable.