An article in the latest Time, elaborating on research published in the American Journal of Political Science, discusses how people infer vitally important personality traits about a candidate from the face alone. What traits? The ones that tend to matter in elections, such as competence, honesty, trustworthiness, intelligence, etc.
And yes, there is a knowledge angle. Here's a graph from the Time piece:
They combined data about voters in the 2006 elections—including their vote choice, political knowledge and TV exposure—with data about the candidates' faces, specifically ratings people gave about how "competent" the candidates were based on looks alone. All told, they analyzed 35 gubernatorial races and 29 Senate races, and they found that "low-knowledge individuals" who watched above-average amounts of TV were about six times more likely to vote for the more competent-looking person than those who watched little TV. They were also much more susceptible than those who had "high-knowledge" of politics. (The Onion headline for this rather unsurprising find would likely read "Ignorant Couch Potatoes Less Likely To Make Thoughtful Decisions.")