For a long time in American politics, you could pretty well guess how someone would vote by their income. Poor people generally supported Democrats; rich people voted Republican. This was true even among whites: In every presidential election since at least 1948, wealthy whites have been notably more Republican than the rest of the white electorate. And throughout the twentieth century, poor whites identified much more strongly with the Democrats than other whites. For decades, a good rule of thumb was: The greener your bank account, the redder your vote.

Then came Donald Trump.