Did Biden is even trip or stumble? It looks more like he just forgot to pick up his foot or his knees buckled under him, both of which are in line with dementia.
Lately, he acts as though “they” have him on some kind of physical regimen; and he probably figured that he could charge up the stairs.
He was moving just a wee bit too fast and failed to raise a toe, enough, having used up what steam he had.