Trump took what existed and fed it and nurtured it and called it good.
I don't think anyone could ever prove such a thing, there were several things pushed by the fringe left that I would say cause this. There are racists out there, the racism of the alt-right, white nationalist whatever you want to call it is "IDENTITY POLITICS". Its bad and its stupid. Its been relatively quiet for some time. Now over the last few years, you have this massive push from the left of what? "IDENTITY POLITICS" and this movement is getting extreme airplay from politicians, celebrities, and the mainstream media. They have sold their soul to go all in on this other side of the coin of "IDENTITY POLITICS" It is a natural progression that this irrational movement on the left, is giving rise to this alt-right, its a fight between idiots, but the left can't seem to call out that on their side.
This new movement has taken several unfactual, IDENTITY-based stands that are causing division. For example, black lives matter, something Obama played up not down, that is emotive, and not based on fact or reality. The lefts broadcasting of emotional, nebulous, protests and bitching is dividing the country, there are racists out there, of course, but this regressive movement has been calling them out from the shadows to fight for several months now.
You can't pick and choose what identity politics is best because they are both WRONG! Trump can act like a petulant child, but the whole left political/msm/celebrity spectrum has more than dipped down to that level, in fact lower in some cases.
Does anyone understand that? Put a vagina hat on and write obscenities on cardboard and claim the president is a mental case, I find it all very ironic.
What Trump may have capitalized on, and what Hillary did not, in fact, she shit on, was middle America ie; not LA and not NYC. Making comments like "deplorable" pushed people into Trump corners. Attacking white America's immutable characteristic of the pigment in their skin, believe it or not, pisses people off. They have put regular white people at the top of an imaginary oppression hierarchy that makes no logical sense, and people need to stop feeding into that nonsense before they complain about the backlash from it!