Atrios wrote yesterday:

I would have no problem casting a vote for a 72+ year old person. It might make me look a bit more closely at who their Veep is, but I'm just not all that concerned with the possibility that the president might get sick or die in office.

I agree, but it's worth underscoring this a bit more. The odds that a man in his seventies would die in office are really quite good. Not "I'd take an even odds bet on John McCain dying in office" good, but good enough that in McCain's case the boilerplate about picking a VP who could take over and do the job needs to be taken seriously. That's hardly an insurmountable challenge for McCain to meet, but it does at least somewhat limit his options. Something like a Dan Quayle pick isn't (and shouldn't) going to fly.