I'm surprised nobody has mentioned the scenario I consider likely: Trump will lose the primary and run as an independent. Then he will be as nasty to the R's as he is to anybody else that doesn't consider him 100 right about everything. That would be bad, but I can see his ego driving him that way.
You beat me to it with your post. That would guarantee another D in the White House no matter who it was.
My state of Michigan went full D from the re electing Whitmer et al + a house and senate that is D for the first time in decades, and a supreme court which will wind up leftist Ds in the majority. Heck even conservative W. Michigan where I live went D.
Gotta hand it to the Marxists from the 60's and 70's. They have been working overtime for 50+ years and have dumbed down a good deal of the population as they control the media, schools, industry, government and even churches. Couple in some willful ignorance, apathy, and voting machinations I'd say America as a bastion of freedom is pretty much over.