I don't think Trump is making intentional steps towards Authoritarianism, as some sort of philosophical belief in the superiority of that as a system of government.
I think he just sees himself as the best leader, so he should have more power to do what he thinks should be done.
I also think he looks at the "strong" leaders around the world and thinks it is better for their countries to be lead by strong leaders who don't have to answer for every little comment or every little action and can take their people in the direction they feel is best without too much interference.
When I think "can't happen here", I'm thinking "one man rule". I don't believe Trump consciously had that in mind. Not sure he even anticipated winning the election.
On the plus side:
We are a long lasting constitutional republic. We don't have any banana republic history.
We have term limits on the office of the presidency.
We do still have a free press.
On the negative side:
Unlike Republicans of the Watergate era, today's GOP will never turn on Trump. No matter what he says or does. This may alter in the future, but we are not there yet.
Trump has no respect for the separation of powers established by the constitution. Thus he tells current and former administration officials to ignore all Congressional supoenas. He does not recognize the Constitutional right of congressional oversight of the Executive branch. Basically, this represents Trump dismissing our very constitution.
AG Barr seems like he is loyal to Trump, and not the Constitution. There may be other such examples in earlier administrations, but this seems the worst case of abandoning the independence of the Justice Dept. I've seen so far.
He has never made one single, heart-felt, effort to be a president for all Americans. He caters to his base, and only his base. In this respect, his is more a cult of personality, and it is clear that is exactly how he wants it.
The strong arm men he does praise, and makes no effort to hide the fact he admires, do not reflect American values. I leave open the possibility that I am simply naive as to what those values are. I may be overly idealistic about what my country stands for. And, indeed, there are many ugly chapters in our history. But when a reporter tells Trump that Putin has reporters killed, and Trump replies "you don't think we kill people too?", that does leave a lot to be desired where me and my notion of what we stand for is concerned. I could offer so many more examples besides Putin.
Those are some of the negatives that seem to erode our democratic institutions.
But, when someone says to me, "can't happen here", I consider that it can actually happen in a sort of accidental way, especially with a party that seems more like a slavish cult. I would never expect to wake up to a headline like "Trump dissolves Congress", no, no overt "one man rule" power grab. But, in increments, in bits and pieces, in response to the Democrats, or with the help of a Justice Dept. or SC amenable to a strong man Executive, I think it possible we can one day wake up to what "can't happen here". Without really recognizing it until there it is, upon us.