Consider this extraordinary finding: In 1960, political scientists asked Americans how they would feel if their child married someone who identified with another political party. Four percent of Democrats and five percent of Republicans reported they would be “displeased.” In 2010, by contrast, 33 percent of Democrats and 49 percent of Republicans reported feeling “somewhat or very unhappy” at the prospect of interparty marriage. Being a Democrat or a Republican has become not just a partisan affiliation but an identity.
