For a fair portion of the American public, Donald Trump is a charismatic leader. I can't feel the charisma, but it seems to be there, and Trump's opponents need to go back to Robert Michel's study of "The Iron Law of Oligarchy" and how the way to break through a bureaucratic oligarchy is with a charismatic, populist leader. Michels ended up supporting Mussolini.
I suspect Trump's populism is shallow and that what we get with him will be a fairly standard Republican bait-and-switch, but with some real payoffs for social conservatives with Supreme Court nominations and such. Still, I don't think Trump or his supporters care much for the Republican Party or know much about traditional conservatism or the US Constitution. If they really get frustrated over checks and balances — and facts about what can and can't be done — then the danger is that "It Can Happen Here" and we get Trump forces out in the streets calling for deportations, jobs, and death to foot-dragging bureaucrats. (The other side to the tremendous difficulty of deporting millions of people is that doing so would create a lot of jobs in the paramilitary-thug line and finally remove the inconveniences of a number of civil liberties and — while at it — civil rights.)
I don't think Trump will be our Mussolini, much less Hitler; I think he'll be Shakespeare's idea of King Richard II: a self-absorbed actor who comes to live the role and, less figuratively, believe his own self-aggrandizing, divine-right, bullshit propaganda. With all his pretty words — beautiful words! — Richard II fell to "hard facts" men after people got bored with his act and over-exposure. ALL TRUMP!! ALL THE TIME!!! will finally bore a lot of people, and bored former fans aren't out of the streets cracking heads and channeling the Will of the Volk to the Leader. They're changing the channel.