Since his selection as Donald Trump’s running mate, Senator JD Vance has performed poorly on most metrics by which we judge vice-presidential nominees. He has never been noted for his charisma, and his attacks and insults have rendered him exceptionally unpopular.

But he was not picked for traditional political reasons, like electoral strength in a swing state or being the ambassador to a needed voting bloc. It may be hard to recall after weeks of talk about “cat ladies,” but Mr. Vance, as much as virtually anyone else in Mr. Trump’s orbit, has tried to put ideological and policy meat on the MAGA bones. Mr. Vance was positioned to be MAGA’s overseer of the so-called deep state, the one who would make sure that, this time around, things would really change. Whether or not he became Mr. Trump’s heir, he would make sure that there would be a Trumpism beyond Mr. Trump.

But can there be a Trumpism beyond Mr. Trump? The idea — which appeals to many on the right who agree with the Trumpist turn on immigration, trade and foreign policy but also see Mr. Trump’s unfitness for office — may be an impossible dream in principle and not only because of Mr. Trump’s practical inescapability.

Mr. Trump’s persona has been the essence of his appeal — his policies matter more for the way they create and sustain that persona than they do for their substantive impact. It is intimately bound up with his anti-institutional posturing, his claim to be the one man who can defeat the system. That is a very difficult thing to institutionalize or even to hand off to a successor.

Indeed, some of the most institutionally destabilizing aspects of populism — its resort to demagoguery, its threats to liberal norms and its association with corruption — may be inseparable from its core appeal.

Populism’s essential criticism is that the apparently neutral forms of liberal government have been hijacked by a class of self-serving elites that are alien to the people from whom, under our Constitution, the government derives its legitimate authority. Right-wing populists tend to emphasize the cultural alienation of that elite class, while left-wing populists highlight its plutocratic remove. But they have a common remedy: a champion who, in the name of the people, will drive those elites from their positions of power and influence and restore a government of the people, by the people and for the people. For that very reason, populist movements from Brazil and Mexico to France and Italy to Turkey and India have been led by charismatic leaders whose authority derives from them personally and not from institutions — because only such a leader can plausibly posture as such a champion.