I have a great many thoughts, most of which are probably wrong, and are driven primarily by my animal brain. But this is my overriding thought:
It's the economy, stupid.
But it's not economic indicators, it's how people feel about their household economy. 9% inflation hit everyone and it hurt. And while inflation is under control now, and there are reasonable arguments about what caused inflation and by how much, short of deflation--which we haven't had (and don't really want as a matter of economics), prices have not "recovered" (or gone back to "normal") after that 9% inflation subsided. Every one of us feels that in our pocket book every day.
So Trump inherits a historically good economy, but not a people feeling good about their household economics.