Partisan voters treat politics and elections like a competitive sports rivalry.

The rise of political polarization in the U.S. government has been mirrored by a similar trend of growing animosity between people who support different parties. But how have these – often uncivil – rivalries arisen? Using data from two representative surveys of Americans in 2010 and 2012, Patrick R. Miller find that partisans treat politics as they would a sports rivalry, with parties viewed in terms of good and evil, with a strong motivation to win at any cost, often independent of policy outcomes. He also finds that not only...