I don't know if it's his breathless exhortations of how much he likes trees and clouds and lakes. I don't know if it's his oddly inhuman (and often inappropriately timed) chuckle. I don't know if it's his completely obvious difficulty relating to people on a human level. I don't know if it's his anachronistic phrasings, like "aircraft" for airplane, or starting sentences with "why," and ending them with "if you will." But there is something that is just off about this dude. There's a reason that it is popular to compare Willard Mitt Romney with C. Montgomery Burns of The Simpsons. Both are deeply out of touch with ordinary people, and both deep down don't really care.
I have figured out who can play Mitt in the movie version of this campaign, though: Ty Burrell of Modern Family. His Phil Dunphy character is equally awkward and clumsy with his speech, they have a similar look about them. But Ty/Phil are far, far more human, so maybe not.