There are lots of things that I seriously hate about Donald Trump. I hate his policies regarding the environment, science, education, women's rights, immigrants and minorities, international diplomacy, etc. I also hate his narcissistic persona, his rude, bullying ego, his nauseating, gold-gilded self-aggrandizement, and his cut-throat, con-artist style of doing business. But the thing that I find WORST about him, the thing that literally keeps me up at night, is his outrageous disdain for the truth.
His pattern of repeating a staggering lie, one easily revealed as a lie by widely available evidence, is downright scary. A key part of that is his strategy for defending his lies: He doesn't try to defend them at all, because they can't be defended. Instead he goes on the offensive, saying that those who are questioning his lies are liars themselves... the dishonest liberal media, the enemies of America. To stay in line with Trump you must reject all rational criticism of him. You must close your eyes and ears to any outside information sources and believe only Trump and the extreme right wing media (e.g., Steve Bannon's Breitbart) that supports Trump's myths.
This creates an extremely dangerous divide between: A) those who trust Trump and reject all other information sources as part of a liberal conspiracy, and B) those who remain open to diverse and reliable information sources including those critical of Trump. Once a Trump follower has crossed that line of believing anything Trump says and nothing that his critics say- YIKES. It's like the plot of "Dr. Strangelove" where the pilots of a nuclear bomber are told to ignore any radio instructions to turn back once they take off on their mission to bomb the USSR, because such instructions might be radio jamming faked by the Russians. It turns out the bomber was sent by mistake by a crazy rogue general, and the Americans try to radio it back, but of course they can't, because their legitimate calls to turn it around are dutifully ignored by the pilots, resulting in global annihilation.
I can imagine a scenario like this: Trump is insulted by cutting criticisms of his environmental policies coming from the scientific community, and then he tweets something like, "The scientists are aligning with Satanic cults to corrupt children!" and "Here are the home addresses of scientists in your town!" spurring militias of heavily-armed Trumpist patriots to break down my door, drag me out in the street and shoot me. It might sound crazy, but these are exactly the kinds of things that have happened in history during other times of ascendant fascism.
To resist this we need to get Trump supporters to start thinking more critically about Trump and thinking less angrily about us liberal types. This will probably requires some diplomacy and understanding, i.e., finding shared values and other little things we can agree on and not always going to straight to the "you're so stupid, how could you vote for such an asshole!" type of arguing. Direct argumentative attacks on Trump supporters, even if they're based on fact, are likely to force a retreat deeper into the bunkers of Trumpism. Of course, being diplomatic with Trump supporters when you really really really hate Trump is much easier said than done. Try, though. Or we're doomed to worsening civil war-like conflict.