My Mom told me she voted against Bob Dole in 96 "because he has mean eyebrows"!!! My response ("we should never have given women the right to vote") was not appreciated. However, if you look at voting trends, it is hard to conclude it wasn't right.
Don't have any facts to back me up, but I'd bet lunch money on the "likeability factor" being the most underrated ingredient in political candidates' winning elections - especially POTUS. (Who do you want to "have to look at" for the next four years?)
In a close race, I believe it's a big factor.