It's obviously a little late in the day, as far as the 2004 elections go, but Alaa at The Mesopotamian posted something to consider that wouldn't have occurred to me:
If you think the President did a bad job and made mistakes and got us all in a mess, then he must not be let off and must stay to clear the mess. Letting him off now will release him from his responsibility to finish the job and tidy up.
If you replace him now with the Senator, then both men will have ready excuses for any future failure. The one will be able to say that he was not allowed to finish his work and the other can say that it was not his fault anyway, because the other made such mistakes as to make any remedy impossible.