Tim Groseclose tells me

Research by UCLA political scientists into the "facial competence" of candidates puts the Republican VP hopeful in the top 5%.

Their paper (http://renos.bol.ucla.edu/AtkinsonEnosHill.pdf ) shows that facial competence explains a significant portion of the vote — about 4% of independent voters in a congressional election.

Here’re some more details: http://renos.bol.ucla.edu/AtkinsonEnosHill.pdf