My take is that it's a bit of a two-way street. "Regular" people resent the elites, yes. But the regular people perceive (correctly) that the elites aren't all that interested in the regular people, either.

If the Democrats had been (and had messaged themselves as being) the party of the working class, they would have drained the swamp that Trump's support comes from. Instead, the message was "if you're working class, and you don't support gay marriage and trans people in sports, and you think that abortion is morally wrong, then you are a moral outcast and we are going to destroy your entire culture." They may have been pro-working-class, but they were pro other things more, and those other things were not big concerns for the working class. And many of the working class took a different stance on the cultural issues than the Democratic leadership.

In fact, the Democrats quit cultivating their base, and so their base walked away from them to someone who at least pretended to care about them.

Nationalist populism harvested that. But there has to be something growing before it can be harvested, and nationalist populism didn't sow the seeds.