I'm distracted at present (sorting out the final edits to "The Delirium Brief", finishing the first draft of "Ghost Engine"), but I can't help thinking that it's about time we all re-read Umberto Eco's magisterial essay on Ur-Fascism, published in the New York Review of Books in 1995.
... The fascist game can be played in many forms, and the name of the game does not change. The notion of fascism is not unlike Wittgenstein's notion of a game. A game can be either competitive or not, it can require some special skill or none, it can or cannot involve money. Games are different activities that display only some "family resemblance," as Wittgenstein put it. ... Fascism became an all-purpose term because one can eliminate from a fascist regime one or more features, and it will still be recognizable as fascist. But in spite of this fuzziness, I think it is possible to outline a list of features that are typical of what I would like to call Ur-Fascism, or Eternal Fascism. These features cannot be organized into a system; many of them contradict each other, and are also typical of other kinds of despotism or fanaticism. But it is enough that one of them be present to allow fascism to coagulate around it.
It's a long-ish essay, but absolutely essential reading. Remember, Eco wasn't just speculating—he grew up under a fascist dictatorship. And if you look around the world today and can't see the relevance of this essay, I suggest that you look again. Not just Trump: look at the BJP in India, the recent coup attempt in Montenegro, the rise of Marine Le Pen in France, Vladimir Putin's Kremlin, and so on.
PS: See also Dr Lawrence Britt on the common core features of fascism.
Update: I am seeing a number of commenters qualify their denunciations of fascism by taking ritual strokes on the dead horse of communism (or "extreme leftism") at the same time. Stop it. We do not currently have a systemic problem with a communist international seizing the reins on power in numberous developed nations; you appear to be twitchily recapitulating the doctrine of false equivalence that the news media in the US have fed you, and it's a distraction and a snare.