Republicans also have two other groups that, unlike the white working class, are increasing in size: voters with a four-year, but not an advanced, college degree, and senior citizens.

Initially, these four-year college grads were torn politically between Democrats and Republicans. They backed Bill Clinton in 1992 and 1996, but George W. Bush in 2000 and 2004. In 2006 they moved back to the Democrats, and in 2008 they supported Barack Obama and Democratic House candidates, but since then they have been gravitating back into the Republican fold and could stay there. Republican Mitt Romney won this group by 51 to 47 percent in 2012, and Republican House candidates won them in 2014 by 54 to 44 percent.

This phenomenon is especially concentrated among whites in this group, who occupy a comparable rung in the occupational ladder now to the working-class Reagan Democrats of 1980, share similar worries and resentments, and have been squeezed economically during the past 15 years. In 2008, according to the American National Election Studies (ANES), Republican John McCain won these voters against Barack Obama by 54 to 42 percent. But by 2012, the margin had widened to 57 to 38 percent — a 7-point swing that is comparable to the margins by which Romney won the white working class.

And there’s a surprising subset of this trend: While African-American support for Democrats doesn’t vary by income or occupation, there is now, according to the ANES surveys, a gap opening up between Hispanics with a high school diploma or less, who supported Obama by more than 70 percent, and those with some college or an associate degree, who supported him by just 55 percent.