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Situating the social basis of Trump's movement in a single class is important to people because of a very literal interpretation of Marxism where there is always a direct 1:1 relationship between class and its politics, but that's not really what M&E thought
M&E's concrete writing about politics talks about fractions of classes having distinct interests and political alliance, and also talks about classes taking political action that's ultimately at cross purposes with their own interests
This is not really entirely the fault of the misinterpreters, because there's a lot of disagreement in the Marxist tradition about how determination of the superstructure by the base works and just how independent is its "relative independence"
The Marxist answer to the question is politics determined by social relations is, "Well, yes and no." Really good Marxist political analysis has a dialectical account of all the interrelations of society and politics, which points out all the contradictions and ironies
As a side note, Marx's words for those who fell out of the organization of society's classes, the lumpenproletariat, the mob, and so forth are not kind; Marxism is not a sentimental disposition to the disadvantaged
