When you're hoping to ascend to the presidency seven years after qualifying for Medicare, folks are going to have some concerns about your fitness to serve four, and more to the point, eight, years in office. So for McCain, a solid VP pick isn't merely a political good or a fun parlor game: It's something of a threshold question. If voters can't imagine the VP taking office, then they probably won't let McCain get there, either.
What are the chances of a VP ascending to the top spot, given that a president is 72 years old?
Looking at the Actuarial Life Table at the Social Security website
and doing the math, it looks like there is a 14% chance of someone age 72 dying within 4 years.
That's one in seven.
That's not the question, though. The question isn't regarding "someone", it's regarding "some male".