The other part that seems to be missing rampant rabid nationalism, as was the case in Nazi Germany.
Do please note that there's are very distinct and important differences between patriotism, and nationalism.
And, no, Trump isn't the problem, but the problem probably beget the Trump presidency.
The problem (the division), as many previous posts have correctly observed, has been with the US for quite some time now.
Looking forward, it is unlikely that this is going to get any better, when you consider that the Democrat party and the left have gone to the extremest hard left, with the mentality of 'by any means necessary'.
The practice of identity politics, victim hood, forced redistribution and excessive political correctness (given that being polite is probably sufficient) aren't really going to help solve anything, much less this problem of a divided and tribal electorate.
Trumped Up: How Criminalization of Political Differences Endangers Democracy. It does, and it isn't going to help either.