To be fair, Trump claims that as president he has "total authority" and total immunity, e.g. such as being able to pardon himself, and many more openly authoritarian expressions. Speaks like an authoritarian, acts like an authoritarian... Also, I can't help but notice his massively dishonest campaign to wrongfully present an election as fraudulent, and running several schemes to overturn the public vote - some of which he is facing charges over. So he's already attempted to cheat democracy.
I think it safe to say that the USA would probably emerge from another four years of Trump still a democracy, but that's because the institutions of state in the USA would be strong enough to constrain Trump. However, it would be even better for those institutions not to be tested in the first place.