Jonah: Unless the boss dies or resigns. That’s a pretty big exception. Let’s see, there’s Ford, LBJ, Truman, Coolidge, TR, etc. A large proportion of our presidents have been vice presidents. I take your point that the ascendancy is not automatic–sitting veeps are notoriously handicapped when they run on their own. But if I really, really wanted to be president, and someone offered me the veep slot on a major-party ticket, I’d be hard-pressed to say no.