MBD, I share your worry. I think the range of possible outcomes is vast. I wouldn’t be shocked if Trump won the nomination again; I also wouldn’t be shocked if he dropped out before Iowa. But I do think Trump has been demonstrably weakened.
The strengths you mentioned are still there, but less so. He’s still a star but, as you note, isn’t going to draw the same overwhelming coverage as in 2015–2016. And his willingness to stand outside and criticize his own party is less appealing after the midterm debacle. Also, he’s less fresh than in 2016, his core issues are less relevant, and others in the party have learned from aspects of his appeal.
It is going to be a crowded field, no doubt. I don’t see Hogan, Sununu, and Cheney all running, however, and doubt any one of them would have a decisive effect on the race.