Jonathan T. Rothwell of Gallup has a paper titled "Explaining Nationalist Political Views: The Case of Donald Trump." The abstract:
The 2016 US presidential nominee Donald Trump has broken with the policies of previous Republican Party presidents on trade, immigration, and war, in favor of a more nationalist and populist platform. Using detailed Gallup survey data for a large number of American adults, I analyze the individual and geographic factors that predict a higher probability of viewing Trump favorably and contrast the results with those found for other candidates. The results show mixed evidence that economic distress has motivated Trump support. His supporters are less educated and more likely to work in blue collar occupations, but they earn relative high household incomes, and living in areas more exposed to trade or immigration does not increase Trump support. There is stronger evidence that racial isolation and less strictly economic measures of social status, namely health and intergenerational mobility, are robustly predictive of more favorable views toward Trump, and these factors predict support for him but not other Republican presidential candidates.From the paper:
In any case, this analysis provides clear evidence that those who view Trump favorably are disproportionately living in racially and culturally isolated zip codes and commuting zones. Holding other factors, constant support for Trump is highly elevated in areas with few college graduates, far from the Mexican border, and in neighborhoods that standout within the communting zone for being white, segregated enclaves, with little exposure to blacks, asians, and Hispanics.
This is consistent with contact theory, which has already received considerable empircal support in the literature in a variety of analogous contexts. Limited interactions with racial and ethnic minorities, immigrants, and college graduates may contribute to prejudical stereotypes, politcal and cultural misunderstandings, and a general fear of rejection and not-belonging.