I don't believe what the NSA is doing is actually barred by the Constitution. As far as I have read/understood it at least. If it is, then you might as well impeach FDR and Wilson post-mortem.
Well, the 4th amendment is;
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
Of course, that's aside from the issue as to whether you think it's acceptable for what purports to be the worlds greatest democracy and an exporter of freedom, to legally permit and continue to allow the warrentless tapping of phones or the alleged storage of trillians of private phone call records. Certainly I don't think the writers would have intended, in writing the constitution, that it could be ignored by the simple development of new technologies.
What about breaking UN Law? When hippie protesters say the Iraq invasion was 'illegal', they weren't kidding. There are international laws established by the UN to prevent superpower nations from invading smaller nations, meaning the invasion ordered by Bush was an illegal act, and therefore he has committed a crime. Would that count within an impeachment?
AFAIK the US does not hold itself applicable to UN law where it doesn't suit it. Both the Iraq war and Guantanamo Bay have been declared illegal (the latter to do with torture) by the UN, and the US simply disregards such criticism. I also believe the US has broken/ignored the nuclear non-proliferation treaty with the abortive development of nuclear 'bunker busters'. For example.
Quick Edit; Deepblue, the US does and cannot
not dictate what the UN needs to do to follow its own provisions; why do you think it is the United Nation
s? Would you accept it if China unilaterally decided Taiwan was in breach of some UN regulation and declared war?