I actually think it has more to do with income and education. Places where there are large concentrations of minorities are, unfortunately, usually places with lower median wages and lower overall education. Trump generally does well with lower income whites, and his popularity grows as you go down the ladder of education.
Racism is also still very much a part of it, but I feel that this result is more based on income/work type and education.
As a white man who once lived in Luis Gutierrez's district, I think this is the best answer so far.
