Research has long shown that a candidate whose photo is deemed more attractive (by people not familiar with either candidate) is likely to win. It turns out this experiment holds true across national lines as well:

A new article in World Politics by Chappell Lawson, Gabriel Lenz, Andy Baker, and Michael Myers provides new and innovative evidence on the importance of looks in running for office (ungated version here). In a very clever research design, the authors asked Americans and Indians to evaluate the attractiveness of Mexican and Brazilian candidates for office. They not only found that Americans and Indians had pretty similar ideas about who was more attractive but also that their judgments predicted the outcomes of Mexican and Brazilian elections surprisingly well. Perhaps American prognosticators for the midterm elections should ask Mexicans and Brazilians about the attractiveness of U.S. candidates to improve the predictive power of their models (edit: actually the obvious implication is to outsource this to Indians).

Now obviously, in races in states or districts with a heavy partisan tilt, partisan identity will overwhelm attractiveness. (Hence Chris Coons' massive lead over Christine O'Donnell.) But it's a shockingly large factor in elections.