Trump is who he is, and always has been. The is a TV star who read his lines badly but believed he was the person in the role was playing. He is a very charismatic speaker who instinctively knows how to connect with those who feel slighted and disrespected. He has always felt that way himself.
He never understood much about politics so when he got elected he thought he was a king who could do anything he wished. He still believes that.
As you say, he isn’t very bright, so he gets surprised and very angry when someone tells him that there are limits to his power or that he is wrong.
But in a more reasonable time, Trump would have been wiped from the scene at his first impeachment trial. By then, all the Republicans and everyone who worked with him knew he was incapable of making sane decisions. The Republicans have had fifty chances since then to take his power away and move on without him. But they are trapped by his appeal to those who feel some power by supporting him. Almost all the Republicans who opposed him lost their primaries. Many of the ones who are winning the primaries are defending the obvious lies Trump tells. They all seem more than willing to get revenge on the country that has become prosperous without them. The world has changed. They didn’t. So they will destroy it. Trump will lead the way.
It’s too late for the Republicans to pull out of this death spiral. Many of them are hoping the Democrats and the DOJ will do that for them. But it may be too late.