To be honest - and I realise fully that I might, just might, be overly optimistic here - I very much doubt he'll be able to put an end to democracy in the US. Not, of course, because he wouldn't do it given half a chance, but because he's too chaotic and incompetent to get it done.
I'm placing my faith in his ridiculous paranoia and demands of personal loyalty here: while I absolutely do believe someone a lot smarter than the Trumpster could accomplish something like this, they'll need co-conspirators. But Trump's style doesn't really seem to accomodate alliances easily. As it it, his WH consists of a variety of factions some of whom have a bit of overlap. You have the Ivanka-Kushner lobby, the alt-righters, the Goldman-Sachsers, a bunch of GOP establishment types, the Russian connection ones plus a few random extra ones. And, so far as it's possible to tell from the outside, the various groups are moving in and out of his majesty's favour constantly. I'm thinking (and hoping) that they're just waaaaaaaay too chaotic to pull anything like an authoritarian system off. Complete breakdown of government, OTOH, well, that could potentially happen.
Coming to think of it, he really does rather remind me of king Joffrey, who, for all his cruelty, seemed to run a similar sort of shop in certain respects.