Some kind of celebrity (ahem, Oprah, ahem) might be able to win the Democratic nomination under present circumstances. But they would need to be respectable rather than disreputable, and run a campaign that accepted guardrails and gatekeepers rather than gleefully destroying them. The wrecking-ball left-wing analogues to Trump that pundits have imaginatively toyed with — an Oliver Stone, a Sean Penn — wouldn’t stand a chance.

But what’s true today might not be true forever. The differences between the Democratic Party’s younger, poorer, browner base and its older, whiter, richer and more moderate leadership are a potentially unstable equilibrium. The anger coursing through left-wing protest politics could find a cruder, more nakedly demagogic avatar than Bernie Sanders. A Hillary Clinton administration could supply various betrayals and compromises or foul up in some disastrous way, encouraging a sense that the professional class that dominates liberalism’s upper reaches needs to give way to a revived (and larger) version of Jesse Jackson’s Rainbow Coalition — a “real American future” analogue to Trump’s “Make America Great Again” appeals.

If Trump has thrived by imitating Europe’s right-wing nationalists, a Trumpism of the left would imitate the left-wing populists of Latin America and Asia — the Chavismo of Alicia Machado’s native Venezuela, or the Trumpian socialism presently being served up by the ranting, trigger-happy president of the Philippines, Rodrigo Duterte.

This may sound implausible, indeed frankly un-American — but so did the ascent of Trump’s National Front-ish politics, and yet here we are.