If they declared him unfit, they would start people wondering who voted for that moron, and suddenly people would realize that there's no possible way 80 million people, especially not Americans, had voted for the clown.
So, they're going to keep their brain-dying puppet around for a couple years. Long enough to do the damage...heck, they haven't got their Vote Rigging Bill on his desk yet, and they need that if they're going to steal more elections, and the other things they need to do to cement their grip on tyranny.
So hang on, this toboggan has a looonnngg way to go before it hits the tree near Suicide Curve.