I can’t think of any examples from history of nations which have had dictatorships take over from democratic systems and then had things improve without revolution or war as an impetus for change. I would be very happy for someone to point out one, but it seems to me that the rot of which trump is a symptom will likely take a significant blood letting to correct, if indeed it is to be corrected.

Really it's a question of where the threshold lies.

The American President is quite elderly, clearly diminished, and the ravages of age are inescapable no matter how beloved you are. However much Americans seem happy to tolerate his particular brand of authoritarianism, the horizon on his rule cannot realistically be more than a decade out.

Is that enough time to consolidate power? If not, is there a successor who can complete his objectives?

Neither seems clear to me, and one can at least imagine a world where things tick back after he exits the political stage.