This all does depend on Bush. He could survive another terrorist attack, or a setback in Iraq or North Korea. Because most people really believe that he is doing the best he can to protect us, and not to protect his political career.
It would be even clearer if he got re-elected in 2004. Then he wouldn't have any re-election to think about. If he is still popular then, he could pick his successor, even if it wasn't his VP. Frist, Condi, even Jeb-
But it's his performance that matters, and I have faith in him.