These skirmishes may be different in substance from those that preceded them, but in the broadest sense they are only the latest manifestation of a half-century trend: the realignment of American politics along cultural and educational lines, and away from the class and income divisions that defined the two parties for much of the 20th century.

As they’ve grown in numbers, college graduates have instilled increasingly liberal cultural norms while gaining the power to nudge the Democratic Party to the left. Partly as a result, large portions of the party’s traditional working-class base have defected to the Republicans.

Over the longer run, some Republicans even fantasize that the rise of educational polarization might begin to erode the Democratic advantage among voters of color without a college degree. Perhaps a similar phenomenon may help explain how Donald J. Trump, who mobilized racial animus for political gain, nonetheless fared better among voters of color than previous Republicans did, and fared worse among white voters.