In this article from the International Herald-Tribune, says,
Democratic presidential candidate Barack Obama laid out list of political shortcomings he sees in the Bush administration but said he opposes impeachment for either President George W. Bush or Vice President Dick Cheney.
"I think you reserve impeachment for grave, grave breeches, and intentional breeches of the president's authority," he said.
Also, what about the horrible violations of the Geneva Convention? All the human rights abuses and torture and all that? Dunno, seems like those might be reasonable grounds for impeachment and/or execution for war crimes. I'm just sayin'.
It's just as well, though, since he didn't really stand a chance anyway.