It’s not really “Trump Derangement Syndrome.” It’s not even “Republican Derangement Syndrome.” The psychological malady might be called “Knowing-that- other-people-do-not-share-my-world-view-makes-me-mortally-anxious-to-the-point-of-insanity Syndrome.”
The issue is dissension. They cannot tolerate dissension. Their psyches will not let them. They must be right, even though they are irredeemably, hopelessly wrong about virtually everything. The only way they can feel like their world view is right is by believing all rational and decent people share their views. When confronted with evidence this isn’t the case, it makes them wildly anxious. In most, the anxiety converts into hostility and rage.
This mentality, so prevalent among leftists, predates Trump. I saw it as long ago as the Reagan and Clinton years. The only difference is that today they’re ready to censor and murder (or applaud murder, as in the case of Charlie Kirk). Leftism hasn’t changed and it will never change. They have always been wrong, and will always be wrong. Intimidation and coercion are, for them, the only way to momentarily shut down the noise of contradiction and error in their psyches.