How segregation leads to racist voting by whites, Ryan D. Enos, Vox, Nov. 28, 2017, available here

But why was this ugly underbelly of American politics so prominent in 2016? After all — as many, many people have noted — a sizable number of purportedly racist Trump voters previous voted for Barack Obama.

A key answer, my research suggests, can be found in "social geography." The phrase refers to how different groups of people, including racial and ethnic groups, are spatially arranged in the geography of America's cities, suburbs, and rural areas. The strength of racially motivated voting in 2016 can be explained in part by the types of people (white or nonwhite, immigrant or native) who lived close to Trump supporters, and, even more importantly, how this social geography had changed over time.