As Jeff Spross points out (and as I've insisted ad nauseum), "the argument that economic distress underlies Trump's success was never that it's the only thing that underlies it." The suggestion that leftists reduce all political questions to class is a tired anticommunist smear that has a long history in right-wing red-baiting rhetoric, and that no one who has ever actually bothered to talk to a Marxist actually believes. And effectively, insisting that leftists are overstating the role of economics when leftists merely insist that economics plays a role is a way of making the equally untenable argument that the economy doesn't play any role at all.
Which, ironically, is precisely the theory that Rothwell's study directly rejects. If liberals read it with an open mind, what they would notice is that Rothwell is actually describing a completely orthodox leftist theory about how the intersection of racism and classism have catalyzed the toxic politics of Donald Trump.
Crucially, Rothwell notes that "two alternative measures of living standards - health and intergenerational mobility - provide support for the idea that Trump supporters are less prosperous than others." Rothwell is unsure about how to understand such phenomenon in economic terms - they "go beyond conventional economic measures" - but speculates, for example, that "material circumstances caused by economic shocks manifest themselves in depression, disappointment, and ill-health, and those are the true underlying causes." It is not particularly difficult to talk about a material / economic basis for health and mobility problems in the community, and those, he notes, are the strongest predictors of support for Trump.
Superficially, this finding is at odds with what the Post identifies as the "widely discussed explanation for the success of Donald Trump": the theory that he has won support with his promise "to curtail trade and other perceived threats to American workers, including immigrants." Neither trade nor immigration seem directly relevant to the health and mobility problems that Rothwell credits for the rise of Trumpism.
But if we simply understand these problems as expressed in a generalized economic anxiety, the study makes perfect sense. And that's where racism comes into play. "Trump is giving his supporters a misleading account of their ills," Rothwell tells the Post - an account that plays on racist / nationalist bigotry. By getting Americans to blame immigrants and foreigners for their general feeling of immiseration and precarity, Trump has successfully channeled their politics away from the actual economic causes.
Obviously even this is a simplification of the role racism plays in Trump support, but nothing here is incompatible with standard left intersectional analysis. On the contrary, this is orthodox leftism to the point of utter banality: capitalists often rely on racism to get people to misunderstand their economic problems. Ironically, the one explanation that Rothwell's analysis excludes is the one that rules out economic anxiety as a cause of Trumpism. Race and class are both at work here, and the sooner liberals figure that out, the sooner they'll stop being liberals.