Race influenced decisions. Blacks favored black students 73 percent to 27 percent, and whites favored black students slightly. But political cues were more powerful. Both Democrats and Republicans favored students who agreed with them 80 percent of the time. They favored students from their party even when other students had better credentials.

Iyengar and Westwood conducted other experiments to measure what Cass Sunstein of Harvard Law School calls “partyism.” They gave subjects implicit association tests, which measure whether people associate different qualities with positive or negative emotions. They had people play the trust game, which measures how much people are willing to trust different kinds of people.

In those situations, they found pervasive prejudice. And political biases were stronger than their racial biases.