So here's the thing. Multiple states have made laws that prevent a candidate being exchanged on the ballot; among them swing states like Nevada, also Wisconsoin and georgia. If they replaced him, they would be eliminated off these states - automatic loss. (well, unless they decide thir rules are onlyfor others and not for them, which.. wouldn't be rare. But anyway.) These laws generally have exception clauses for "death and official incapacity". Which means the only way to change and remain on these ballots, except for some trickery, is.. well. So yeah, the only way to change candidates is to official humiliation in a constitutional process of officially declaring him kale. Difficult.