- a woman
In a rational world, McCain would have to give up his attacks on Obama's experience, since Palin is younger and has served as governor of Alaska for half the time that Obama has been in the U.S. Senate. In other words, she's much less ready to step into the Presidency than he is. But we don't live in a rational world.
An irrational world has its uses, though. Imagine an oblivious apolitical citizen stumbling upon them on the campaign trail.
"Hi, I'm Sarah Palin. I'm running for Vice President. I'd like you to meet--"
"Nice to meet you, young lady. Is this your dad?"
Is Palin enough of a frothing wingnut to galvanize the crazy GOP base? The CNN story doesn't mention any evangelical cred, and I've only known her name for a few days, so I can't tell. Her resume, as opposed to her sex, says that McCain has doubled down on drilling oil wells as his winning issue.
Update (8/31): For another Michael Palin reference (in the headline and waaay too contrived), see "Biff called Wanda".