Imagine that the US President really is (mostly) a figurehead. He gets briefed by folks where the decision is already made, by them. The briefing is couched such that only one option appears viable. He's not making decisions. He appoints about 4,000 individuals to positions, 1200 of which require Senate "confirmation" (rubber stamp usually).
No President has any clue about more than maybe 30 of those. They are made for him, some campaign donor gets Ambassador to Thailand etc.
In other words, his staff makes every decision for him, and perhaps lets him think he's doing something. One could argue he would at least name most of his staff, probably. But if this is the case, anyone could be President if they can smile for the camera and sound semicoherent most of the time. If not, they keep him in the basement of the WH.