When Elizabeth I was asked why she wouldn’t designate a successor, she said people worshipped the rising, not the setting, sun. Trump almost certainly understands that, which is why he persists in talking about a third term.
Consider what this means for J.D. Vance. He won’t be able to start his campaign until very late in the process. Neither Trump nor the base will forgive him if he puts any distance at all between himself and the president. In fact, I suspect he will have to portray himself as a puppet for Trump in order to get the nomination. That will be awkward, to say the least.
Where does that leave Vance if Trump is viewed as a failure by a majority of Americans? Oh, right. He’ll still have the military and the DOJ. That might be enough.