Imo, and you can be as dismissive as you want about this, but I think that Trump's support is hardened because his voters are in a "this is war" mindset, due to the media and Russia. I saw this on the left w/ Bill Clinton. I genuinely don't think that - in a vacuum - most would say they truly support what Trump is doing right now or what kind of President he is. They simply do not want to cede anything to liberals, elites & the media.
He can't win another election w/ just his hardcore supporters, though. Indies who were just voting against Hillary or voting for a single issue aren't going to go for this too much longer. "Trump fatigue" will be a real thing in a year or 2.
And yeah - that's a prediction. Just like the many I've made that have panned out perfectly.
look it's impossible to predict an election 4 years out, lots of things can change, numbers can go up and down. however I recently saw that trump still has the majority of support in all counties he won in 2016. Meaning even today he'd still have a good shot of winning the election.
i also don't dispute much of the "dug in" mentality. But I dno't think that's exclusive to trump supporters.

