Don't think it really matters, in the big picture, who can sell the most BS wins. They don't call Clinton slick willy for nothing. Bush I and Dole had little to no charisma, and stood no chance.
Bush II hmmmm, you pit him against Gore who is a goofball and tries to take credit from everything under the sun, doesn't surprise me
Bush II , you put him against Learch Kerry who is about in touch with the average American as Stalin, doesn't surprise me either.
Obama vs McCain, again a case of lack of charisma, I don't like Obama, but he could see an ice box to an eskimo.