Faced with a choice between John McCain and Barack Obama, voters in 2008 were swayed by the familiar play of factors—party identification, policy preferences, and economic conditions—but also, we find, by ethnocentrism, a deep-seated psychological predisposition that partitions the world into ingroups and outgroups—into “us” and “them.” The effect of ethnocentrism was significant and substantial, and it appeared over and above the effects due to partisanship, economic conditions, policy stances, political engagement, and several varieties of conservatism. Two features of Obama were primarily responsible for triggering ethnocentrism in 2008: his race and his imagined Muslim faith. As such, we demonstrate that ethnocentrism was much more important in 2008 than in the four presidential elections immediately preceding 2008, and we show that it was much more important in the actual contest between Senator McCain and Senator Obama than in a hypothetical contest between Senator McCain and Senator Clinton.