“Populism as a movement functions as a response against the ‘establishment’. It’s a disruptive reactionary force.”
This is a side-note, really, but the latter part of that isn’t defensible as so general a statement. Populism is anti-elitist. The character of it beyond that is entirely dependent upon the context. Right-wing “populism,” including the fascist variant, is a faux-populism. Fascists rail against the Establishment but it’s political theater, a means of assuming power. Given that power, they only destroy democracy and its institutions. Successful fascist movements certainly don’t send conservative elites to the guillotine; they ally with them (and generally find them to be enthusiastic allies as well). Real populism, the kind that isn’t anti-intellectual, the kind that rails against genuine abuses by genuine elites, is in no sense “reactionary”; portraying it as merely “disruptive,” however, is reactionary.
The quest for a generalized definition of fascism is no longer the academic battlefield it once was. The game-changer in that back-and-forth occurred 20 years ago and was the fellow you cite, Robert Paxton. The rise of Trump has spurred a wide range of articles and commentaries considering the question of Trump and fascism. Some are thoughtful, many are poorly informed. I’ve contributed to the pile myself:
And Trump’s connection to actual fascists:
There is, as I see it, no serious case that Trump is a fascist but he’s certainly protofascist. The movement behind him, which long predates his political rise and is far more important, does contain a major protofascist/fascist contingent, which has increasingly penetrated and captivated “mainstream” conservatism to the point that such conservatism is on the verge of extinction. Those who, in order to defeat the characterization of Trump as an outright fascist, too strongly insist Trump is merely a “right-wing populist” do a real disservice; this particular species of right-wing fake populism is the fetal stage of fascism. It has developed nearly every characteristic except the more extreme lusts for violence against enemies.
