I've blogged before (the sad state of blogger's block that hit me a while ago makes it really easy to find) that I think Bush and Cheney will probably not serve out their terms. Shoving that argument firmly to one side a moment, let's say that's true. After all, in 1974 no-one really expected Agnew to bite the dust before Nixon. Especially, no-one expected Agnew to bite the dust over a separate scandal completely unrelated to Watergate.
Anyway, the situation is all neatly covered (or not) by the US constitution. You'd really wonder how those Democrats seeking the nomination for 2008 would feel if they woke up one morning to watch President Pelosi being sworn into office. We'd probably be able to hear the gnashing of teeth all the way cross the Pacific.