We’ve had third parties over the years, and sometimes, at moments of great instability like the 1850s, fourth and fifth and sixth parties. But they don’t last. The reason for that is the remorseless logic and inevitable direction of Duverger’s Law. Let’s say Mr. Trump’s Patriot Party — or whatever he calls it, since there might be legal issues with that name — runs congressional candidates in certain targeted districts. And the party wins, say, 17 seats. Pretty good, for a new party.

But given that Trumpy candidates aren’t likely to do very well in blue or even most purple districts, the net effect is probably going to be that they’ll be unseating 17 Republicans. And what’s the effect of that? To ensure that the Democrats — the radical left socialists! — hold a House majority.

Likewise, let’s imagine the Patriot Party running a presidential candidate, most likely Mr. Trump himself, while the Republicans and Democrats run their candidates. Mr. Trump will get a lot of votes. He may even beat the Republican, as indeed Roosevelt bested Taft in 1912. But he will split the center-right vote in two, while the Democrat will get a typical 48 or so percent. Result? The Democrat will carry a lot of states with a plurality and thus win the Electoral College. And in the long run, the inexorable machinery of Duverger’s Law will ensure that the Patriot Party is folded back into the Republican Party.