It’s widely appreciated that Trump appealed especially to non-college-graduates and older voters. There’s also an ethnic angle. Groups with high degrees of social connectedness and respect for order — Mormons, Dutch- and German-Americans — were largely immune from his appeal. People without such ties, whom he called Thursday night “people who work hard but no longer have a voice,” were drawn to him.
Groups that respond positively to raucous disruptive appeals rallied to Trump: Scots-Irish along the Appalachian spine from western Pennsylvania to northern Alabama; and Italian-Americans, half of whom live with 100 miles of New York City. If you draw a map of counties where Trump topped 50 percent by May 4, the great bulk of them are along that diagonal and within that circle.
At least within Republican politics, and maybe the country, the division is no longer North-South, but instead North+South+Border jaded and hardened versus Upper Midwestern and Intermountain pleasant. The very people who still have the social preconditions which Trump seems to want for everywhere are the very people who were coldest to Trump’s campaign. For example, heavily Dutch-American Sioux County, Iowa is the beaux ideal of Trump policies, but Trump only got 11% of the vote in the Hawkeye Cauci, Cruz won it with 34%.