Conservatives must be squirming about Bush's position on the Iraq War. They will not let the President drag them through another election with the Iraq War hanging over their head, blame and guilt dampening their message and assuring their defeat. If there is an impeachment, it wouldn't surprise me if the Republicans began the process.
Joe Scarborough (video) provides a stellar example of a conservative losing his nerve and beginning to speculate about impeachment. I recognize that this fantasy would take a massive crumbling of party loyalty, but Mr. 29% doesn't have a lot to offer in political terms these days. It would easily be the greatest real tragic fall in my lifetime.