I don’t buy that all these racists that wouldn’t have voted otherwise came out of the woodwork to support Trump.
Neither do I, but I think you underestimate the number of racists if not outright white supremacists that vote for Democrats, and even voted for Obama. In terms of presidential candidates, neither McCain, Romney, nor Obama really made a big deal out of race. They were all pitching the same sort of “we all get along and nobody owns anybody else” society, just with different tax rates. From my experience in some deeply racist regions of the country, if racism is a big selling point for you, all of those candidates looked pretty much alike in terms of race. Yeah, one was black, but all of them would lock you up if you firebombed a church, so tomayto tomahto on the race issue. So you decided based on secondary issues – economics, usually. And that’s where Democrats usually pick up the uncommitted racist vote.
Trump was different. We haven’t had a candidate as overtly racist as him in generations. All those Obama-voting racists went to Trump. No respectable Democratic candidate could have picked them up. The only solution was to get non-racist people who didn’t vote before to come out of the woodwork, or non-racist Republicans, and that didn’t happen–not in the right states at least.