"It wasn’t her appearance per se” that soured people on Palin, Heflick said in an interview. “It was the effect her appearance had on their perception of her competence and humanity. Those variables made people less likely to vote for her.” ...
So at least in this sample, it was Republicans and independents who were internally debating Palin’s suitability for the job. The study suggests that their confidence in her abilities may have decreased the more they focused on her looks — and thus, in feminist terms, objectified her.
You can read about the study's methodology in the article. It's a sad world, however, where the attractiveness of a male candidate potrays youth and vitality (i.e., JFK and Obama) and, to the extent this study is generalizable, the attractiveness of a female candidate portrays incompetence.
(h/t Ben Smith)