1) Facebook made easy to find the "latent Klansman" in Wisconsin and Pennsylvania.
OR
2) There are large swaths of working class white people in the middle of the country unhappy with how their economic prospects have been trending in the last 10 years.
https://twitter.com/stevenvmiller/status/1014967443813519360
https://github.com/svmiller/earr
https://www.vox.com/identities/2017/12/15/16781222/trump-rac...
https://www.bostonglobe.com/opinion/2018/04/25/debunking-ele...
https://www.thenation.com/article/economic-anxiety-didnt-mak...
>We created a stereotyping scale which measures views like believing people of color are more violent or lazier than whites, but it was not included in our final models because it did not predict voting behavior.
Let's just ignore the thing that disproves our premise.
The lousy job market cost Hillary the presidency too.
Trump is a protest candidate. His supporters are not knuckle-dragging troglodytes who crawled to the voting booth, drooled on the voting machine, and grunted "make America great again!". They are rational beings, who looked back at Obama's presidency, and were not impressed.
Yes, employment improved during Obama's tenure, but new jobs have been low-paying and low-status. No bankers went to prison. The corporate-friendly policies of the Obama era didn't earn him friends in the working class. And Hillary promised more of the same.
Targeted advertising can prod racists to vote, as the OP suggests, but that only works if the non-racist voting majority feels some hope.