Hitler, Mussolini, and Franco were wicked and were highly competent at being wicked. They were not simply autocrats. They were "totalitarian" -- maintaining total control over every level of society, from newspapers, to trade unions, to youth groups. In contrast, non-totalitarian "strongmen" might be bloody tyrants, but generally have little interest beyond control of the government. Is Donald Trump is either category? Is he a strongman? Totalitarian? Or something else?
Totalitarian leaders, before controlling everything around them, master self-control. They can be nuanced. They can charm. They have mastery of every level of society. They are informed. They can set out demonic strategies while keeping their tactical cards close to their chests. They have ideologies which they can articulate clearly with mesmerizing oratory.
Trump cannot control even himself. He cannot speak a coherent sentence which is not on a Teleprompter. He has no ideology. There is no "master plan."
He is authoritarian. He is a narcissist and demagogue. He is also a fool.
The term "genius" is usually generally used as a term of approbation, as if intelligence is a virtue. It isn't. Intelligence is a talent, like running fast: one can run fast to do good things, to do bad things, or just to run. There are evil geniuses. The Nuremberg defendants were given IQ tests and almost all had exceptionally high scores. They were geniuses.
I don't know Trump's IQ. He certainly has talent as a showman and has been able to manipulate discontent. But he is a boob who has not mastered the critical elements of statecraft and has proven woefully ignorant of international, domestic and military affairs. Even if one likes his bluster, it is likely that much of the harm he would bring about will be because of impulsivity as much as by design.
Europeans, aggravatingly, often assume their superiority over all things American. Contrast this with our own high notion of "American exceptionalism." While European superiority and American exceptionalism are overstated forms of regional conceit, I think it is true to say that European tyrants are better at tyranny. Our home grown attempt at authoritarianism would be altogether laughable, except that, in his stumbling and bumbling, he might actually prove as destructive as his European counterparts.