Certainly, Trump’s an authoritarian nationalist who’s a symptom of structural problems in the US. But he’s a fascist too.

If you look hard enough at instances of any type, you’ll find differences between them. Whether those differences are essential or peripheral depends largely on your interests. For instance, are Poodles and German Shepherds both dogs? According to some scientific measures, yes, but if you’re interested in the behavioural or phenotypical differences, you might not lean on the abstract sense in which these animals belong to the same overall type. Subtypes develop because of differences in breeding, but the ideal type “Dog” still applies broadly to both.

Hence, words change their meaning over time and gain multiple senses. In a narrow, historical sense, Trump may not be a fascist, if only because he wasn’t alive in the WWII period. But Trump can still be a fascist in a broader sense. That broad sense might not interest everyone and might have drawbacks, but the sense is valid if it's useful for certain purposes. Compared to average American politicians, Trump’s a flaming fascist, not just a vague authoritarian or nationalist since he excels at Hitler’s style of populist, racially charged demagoguery and scapegoating. Sure, Trump’s boasted that he’s an insider who can fix the American system, but he’s also an outsider from Queens who explicitly aligns with aggrieved rural folks against the establishment.