Reince Priebus, the chairman of the Republican National Committee, delivers a speech at the G.O.P. Convention, where Donald Trump was awarded the Party’s nomination. Photograph by Alex Wong / Getty

There is so little discipline in the Donald Trump campaign (and even less shared long-term interest) that we already know a fair bit about what has transpired in the past forty-eight hours inside the Trump Tower penthouse. According to the Washington Post, Trump was holed up in his home with a group of what are, politely, called “advisers” but seem more like characters in a tossed-off screenplay, each representing a cliché of cravenness. Chris Christie and Rudy Giuliani were reportedly there. While technically different people, in this context they were redundant: two reckless gamblers who had lost everything until Trump gave them a long shot at getting their power back. Kellyanne Conway stood in for the amoral professional operative. Stephen Bannon, the Breitbart chief, was the whisperer whose interests are served by chaos. (His business appeals to a narrow target audience of angry white conservatives and flourishes on outrage.) We can ignore Donald, Jr., and Hope Hicks, who have shown themselves to be ineffective loyalists with no perceivable judgment independent of Trump’s. The most telling detail in the reports has been the absence of Ivanka Trump, the one person who seems intent on preserving the value of a non-loathsome version of the family name. (Her husband, Jared Kushner, reportedly violated his Sabbath and was present; Ivanka turned down opportunities to defend her father.)

Of all the people in the room, however, Reince Priebus, the head of the Republican National Committee, was the most interesting, because he was the one person representing something beyond his own interests. Priebus long ago made it clear that his obligation is to the Republican Party and not to the United States, or even to Trump. This made his set of choices far more complex than those of anyone else there.

For a moment after the release of the vile “Access Hollywood” tape, this group seemed to have coalesced around the only reasonable strategy. The Post reported that Christie, Conway, Bannon, and Priebus were aligned, and quoted a Republican close to the campaign saying, “Priebus and Christie just went at him and said, ‘Donald, you’re going to have to apologize for the first time in your life, right now.’ ” Soon, though, the plan was peak Trump: a non-apology apology and a promise of scorched-earth ugliness. Conway disappeared from public view. Giuliani doubled down on his shamelessness (his twin, Christie, surprisingly disappeared). Bannon himself was silent, but his site blasted outrage at the Clintons, promoting a (http://www.breitbart.com/2016-presidential-race/2016/10/09/breitbart-news-exclusive-video-interview-bill-clinton-accuser-juanita-broaddrick-breaks-describing-brutal-rapes/), who accuses Bill Clinton of rape. (Clinton’s lawyer has denied that accusation in the past.) Retweets of that story comprised half of Trump’s sparse communication yesterday.

Priebus must have felt very lonely. I look forward to learning if he screamed or fell quiet as he realized that Trump, supported by his coterie of deplorables, had decided to lose this race in the way that would be most damaging to the Republican Party. By late Saturday, according to the Wall Street Journal, Priebus began to end the shotgun marriage between the Trump campaign and the Party’s election apparatus, instructing staff and venders to try to save the House and Senate and forget about the Presidency.

There is no need to feel sympathy for Priebus. How in the world did he not expect a tape like this—a thousand tapes like this—to come out precisely at this moment? He may not have wanted Trump to be the nominee, but he played the leading role in normalizing this odious candidate; he has much to answer for. Still, it seems likely that whoever ran the Party at this time would have behaved similarly. Political parties are, essentially, built to insure disastrous outcomes like this one.

In America, political parties were not developed to celebrate and reinforce a shared ideology. Precisely the opposite. Parties exist to create conditions under which people who disagree with one another can work together to achieve their personal ambitions. There is no inherent reason for libertarian businesspeople, religious values voters, and white nationalists to belong to the same party, and it wasn’t that long ago that they didn’t. The same can be said for union members, social progressives, and environmentalists. In countries with parliamentary systems, each of these groups has its own party that only forms alliances with the others after an election reveals their relative strength. But in the U.S., with its strong Presidency and winner-take-all elections, the two-party system evolved to solve something known as the collective-action problem. There is no single interest group that has a clear majority of American support. So, each subgroup needs alliances to gain power.

One of the party’s key functions is as a promise-enforcer. The key problem with alliances is that each member has a strong incentive to free-ride on every other member. If I’m a Christian conservative running for Congress, I can tell libertarian funders that I support their vision so that I get money from them now; then, after the election, I vote to tax the rich. If there is a party, each member is assured of a carrot and a stick: loyalty will bring more support and disloyalty will mean banishment. Parties get self-interested people to act collectively. In game theory, one way to do this is called pre-commitment. Each member must do something to definitively limit his or her future options, to prove that they won’t abandon the team after they’ve received lots of goodies. White prison-gang members, for example, put Nazi tattoos on their necks and faces, insuring they cannot easily leave the group and find support elsewhere, thus earning the promise of protection.

When it became clear that Donald Trump was going to be the nominee, every structure within the Republican Party pushed for one outcome: support him. This was not despite the fact that most of the Party leadership opposed him, it was precisely because of it. Getting behind a man whom they hated must have looked like the Party performing its core function. When Priebus threatened to punish those who opposed the candidate, it was the Party, not Trump, that Priebus was defending. His actions, at that time, puzzled many on the outside but meant that the Party supported him more intensely than ever. A Politico story about Priebus’s inevitable triumph in an unprecedented reëlection as the R.N.C. chair explained, “In interviews and email exchanges with 50 members of the Republican National Committee, dozens of the party’s leaders indicated that they wouldn’t blame Priebus for the second straight presidential defeat on his watch. Rather, they credit him with turning around a broken party apparatus, raising boatloads of cash and standing by the party’s polarizing nominee despite fierce headwinds.”

Perhaps if Priebus had known, in July, that by October his Presidential candidate would have close to no chance of winning and would be in open insurrection against a quarter of Republican senators and the Speaker of the House, he might have acted differently. But my guess is that he wouldn’t have. Just look at what he is doing now. He has figured out how to simultaneously drop Trump by cutting off ground support and also stand by his side. He is giving down-ballot candidates what they want and also giving Trump what he wants. To every future Party member, Priebus has performed the ultimate pre-commitment, even more than if he tattooed an elephant on his forehead. He—and the party he runs—will find a way to support Republicans no matter who they are, no matter what they believe.