Two guides I’ve found to answer the question are Umberto Eco’s 1995 essay, “Ur-Fascism”, and now a new German collection of academic essays, Wenn das Gestern anklopft (“When Yesterday Knocks”), edited by Philipp Ruch and Thomas Weber. Reading Eco, the parallels between Trump’s methods and fascism become obvious; but the German collection persuaded me that his worldview and aims are distinct from fascism.