They wont have to - Spector has already announced he's going to do this
My hunch is that this will NOT be a very good fishing trip for impeachment tidbits.
Bush seems to want this fight, and Congress seems to want to avoid it --- hence the red-herring issue that is being served up --- the "we can't have the military in charge of the CIA" argument.
I do think the democrats hope to use the NSA surveillance program as an impeachment issue, but for some reason they don't want to draw too much attention to it right now. And some Republicans want to avoid it too . . .