His geographic pattern of support is not just about demographics — educational attainment, for example. It is not necessarily the typical pattern for a populist, either. In fact, it’s almost the exact opposite of Ross Perot’s support in 1992, which was strongest in the West and New England, and weakest in the South and industrial North.

But it is still a familiar pattern. It is similar to a map of the tendency toward racism by region, according to measures like the prevalence of Google searches for racial slurs and racist jokes, or scores on implicit association tests…

In many of these areas, a large number of traditionally Democratic voters have long supported Republicans in presidential elections. Even now, Democrats have more registered voters than Republicans do in states like West Virginia and Kentucky, which have been easily carried by Republicans in every presidential contest of this century. As recently as a few years ago, Democrats still had a big advantage in partisan self-identification in the same states.

But during the Obama era, many of these voters have abandoned the Democrats. Many Democrats may now even identify as Republicans, or as independents who lean Republican, when asked by pollsters — a choice that means they’re included in a national Republican primary survey, whether they remain registered as Democrats or not.