Jamelle Bouie nicely summarizes Umberto Eco's list of the qualities necessary to be a proper fascist.
They are: A cult of “action for action’s sake,” where “thinking is a form of emasculation”; an intolerance of “analytical criticism,” where disagreement is condemned; a profound “fear of difference,” where leaders appeal against “intruders”; appeals to individual and social frustration and specifically a “frustrated middle class” suffering from “feelings of political humiliation and frightened by the pressure of lower social groups”; a nationalist identity set against internal and external enemies (an “obsession with a plot”); a feeling of humiliation by the “ostentatious wealth and force of their enemies”; a “popular elitism” where “every citizen belongs to the best people of the world” and underscored by contempt for the weak; and a celebration of aggressive (and often violent) masculinity.
The follow up question: Is Donald Trump a fascist? Bouie says Trump uses "rhetoric of fascism." Trump's policies are developing along fascist lines. "The only thing left is the violence," Bouie concludes.
It's hard to say too many bad things about Donald Trump, but it may be premature to certify him as a fully-formed fascist. Yes, he talks like one, but he doesn't have a developed fascist symbolic system–uniforms, insignia and all the other elements of an aesthetic–through which he could build an organization to deploy violence as a political tool. Propaganda by itself won't do the job. On the other hand, it took the Nazis a while to develop a fascist aesthetic of their own.