And he’s coming at all these issues, crucially, from a vantage point of privilege — which his critics keep highlighting as though it discredits him, when in reality it lends his populism a deeper credibility. He’s the Acela Corridor billionaire (albeit tackier than most) who promises to reveal what the elites are really up to, the crony capitalist who can tell you just how corrupt D.C. really is, the financier who’ll tell you that high finance can afford higher taxes. It’s precisely because he isn’t a blue collar outsider that he may seem like a credible change agent: Because he knows Wall Street, and because he doesn’t need its money to campaign, it seems like he could actually fight his fellow elites and win.

He won’t, of course, but it matters a great deal how he loses. In a healthy two-party system, the G.O.P. would treat Trump’s strange success as evidence that the party’s basic orientation may need to change substantially, so that it looks less like a tool of moneyed interests and more like a vehicle for middle American discontent.

In an unhealthy system, the kind I suspect we inhabit, the Republicans will find a way to crush Trump without adapting to his message. In which case the pressure the Donald has tapped will continue to build — and when it bursts, the G.O.P. as we know it may go with it.