Holmes is wrong.
What he calls "rural, working-class voters" are actually "low skilled white voters scared about losing their socioeconomic power to non-whites". Nobody can play on those fears and galvanize the support Trump has without demonizing "them". "They" are the non-whites taking jobs for low pay. "They" are the non-whites gaining political power as demographics shift. "They" are the elites making a living from modern skills rather than low skilled labor. "They" are the members of the gays/trans communities getting equal rights.
Trump's base adores him because he embraces the complaints of the downtrodden white person who is losing the only shred of power they have: white privilege. The prospect of that privilege going away is terrifying to these people who literally have nothing else going for them. Low skilled rural whites understand the moment that privilege goes away, they are nothing more than the very people they look down upon and treated so poorly. So it is literally impossible to play to those fears without demonizing the people they are afraid of.
Trumpism is white grievance politics, period.