Shankar Vedantam argues that partisanship is the new racism.
When partisanship is seen as a form of social identity—I’m a Democrat because people like me are Democrats, or I’m a Republican because people like me are Republicans—we can understand why so many blue-collar Kansans are Republicans and why so many Silicon Valley billionaires are Democrats, even though each group’s rational interests might be better served by the other party. Partisanship as social identity helps explain why, if you’re a black man in America, it’s really, really difficult to be a Republican. Same goes if you are a white, male, evangelical Christian in rural Texas who supports Barack Obama. Social identities are not deterministic—there will always be some black Republicans and some born-again Christians who are liberals—but most of us stick with our social tribes. Any liberal who supported George W. Bush’s adventure in Iraq would have been ostracized by his friends. A conservative who feels Barack Obama is a cool president will be made to feel like a traitor at church.