I hate to say this, because it would be a mortal sin, but I believe if this happened, some one would take matters in his, or her, own hands.
I don’t think anyone will even be upset - remember the frog in the pot? When the heat i9s being turned up gradually, he doesn’t notice he is being cooked, until he is completely done.
I think we are halfway cooked already and have no strength to even jump out of the pot, much less do anything else.
This possibility is always there, no matter who the POTUS is. There are probably a finite number of assassination attempts, just on President George W. Bush, that the general public will never, ever really know about.