Mr. Stewart has since retired from the ring, having replicated himself a dozen times over on every channel, each copy smugger than the last. But Mr. Carlson, too, has triumphed. He now hosts one of the top-rated shows on Fox News, where he has become a shouty populist version of his former mini William F. Buckley Jr. persona — much closer to the trollish partisan Mr. Stewart accused him of being than he ever was in his “Crossfire” days.

And the rest of the movement has evolved — or devolved — alongside him, from the organizers of the Conservative Political Action Conference who invited Marion Le Pen and Sheriff David Clarke, to the campus conservatives who’ve doubled down on their strategy of inviting Ann Coulter and her spiritual descendants to speak to the very audiences likely to be most outraged by them. For many campus conservatives, the invitations are driven by a sincere desire to give their values an airing and set off debate. It is, of course, also fun to annoy people who disagree with you.

Ironically, or perhaps predictably, tonal tensions are escalating at a time when actual policymaking has ground nearly to a halt, with budgets and major legislative packages hopelessly stalled in Congress after Congress. The attempt to find common ground over the “Dreamers” — the group of undocumented immigrants who came to the United States as children — for instance, ultimately involved a brief shutdown of the federal government and a near miss of one. The left labeled the right racist; the right accused the left of hating America. No substantive policy change resulted.

So maybe it makes sense that political squabbling across much of America has become increasingly aesthetics-focused and content devoid: It’s no coincidence that at the moment the alt-right leader Richard Spencer was sucker-punched on camera, he was explaining the elaborate in-joke signaled by his Pepe the Frog lapel pin. Nor that when Russians allegedly tried to meddle in the last presidential election, they chose to do it in meme form, with Facebook ads featuring Jesus and the Devil arm wrestling over the prospect of a Hillary Clinton victory, or promoting “Buff Bernie” pro-L.G.B.T. coloring books. Differences remain as fundamental as ever, but the way we talk about them is so superficial as to have become incoherent.

But that has done little to restrain the all-consuming ferocity of the fighting. Nor have the consequences been restricted to the internet. The tonal differences go all the way to the top: If Barack Obama’s “cling to guns or religion” statement was a perfect distillation of the smug style in liberal politics, Donald Trump is impeccably suited to an increasingly post-ideological Republican landscape where the point-scoring is the prize.

One of the primary reactions to this new framing of the political debate has been exactly what you’d expect: Many sane, self-respecting people no longer want anything to do with either side. Barely half of the respondents to the last round of Gallup’s long-running question about partisan affiliation could bring themselves to pick a party at all, with just 28 percent identifying as Republicans and 27 percent as Democrats. (Happy start of midterm season!) And even when Gallup tried to force people into bicolor boxes, by asking the 46 percent identifying as independents which way they lean, the totals still come only to 46 percent on team red and 44 percent on team blue.