Mike Segar / Reuters

Several months ago, I discussed the science behind endorsing Donald Trump with Kevin Zollman, an associate professor at Carnegie Mellon University who studies game theory. It was a different time: Jeb Bush had just thrown his support behind Ted Cruz, and Chris Christie’s fawning support for Donald Trump made him the punchline on Saturday Night Live and pretty much everywhere else. Back then, endorsing Trump was weird enough to warrant calling a professional strategist for an explanation.

Politicians want to look prescient, Zollman told me, so early endorsements like Christie’s carry a special power. But they also want to be right: When they give their support, they give a lot of thought to how their peers might vote, perhaps even more than the bona fides of the candidate at hand.

After the recent release of a 2005 video clip that revealed Trump making lewd comments about women—and recent allegations of sexual assault against the Republican nominee—the process has been thrown into reverse. Over the weekend, a slew of Republican elected officials withdrew their endorsements for Trump, calling his comments unacceptable. Trump took the fight to Twitter, hinting darkly that “hypocrites” would get their comeuppance. Later, some GOP legislators who had called on Trump to step down said they’d still vote for him. Could game theory explain this back-and-forth?

I called Zollman to get his thoughts. He theorizes the deluge of Republican withdrawals came from what’s called an “information cascade,” the sudden realization that nobody is happy with the state of affairs. And since that flow has started, Zollman says, Trump is moving very quickly to shut it off.

Our conversation has been edited and condensed for clarity.

Andrew McGill: After the release of the 2005 Access Hollywood tape, we’ve seen a slew of Republicans withdraw their endorsement of Trump. But a few of them have straddled the line and even tempered their “un-endorsements.” Why?

Kevin Zollman: The idea is, you don’t want to be left out there alone. A number of people predicted that [the tape] was going to be the watershed moment, that the whole party was going to un-endorse him and he was going to become a lame duck. And it looked like that was happening—but then it stopped. When you see a couple of people “re-endorse” Trump, they’ve realized that’s the direction of the party, and they don’t want to be left out in the cold.

And there was this group of people that didn’t exactly un-endorse Trump. What they said was, “Trump needs to step aside.” And I think that was actually a strategic move. They leave themselves wiggle room to make a statement that could later either read as, “I unendorsed him early,” if that’s the way the wind blows, or “I never unendorsed him.” You could always claim to have been in the majority, no matter what.

McGill: What got this ball rolling? It seems like the early rush of un-endorsements came all at once.

Zollman: It’s something called an “information cascade” in economics. You might have a bunch of people who privately want one thing, but feel they can’t declare that. Once a few people start declaring it, the rest say, “Oh, I can too.”

I think a lot of people thought the tape was just the beginning, and that the debate was going to go horribly for him, and the [congressional Republican] phone call on Monday was going to end with Paul Ryan just completely un-endorsing him, and they just wanted to look like they got out ahead of this. You had a couple people who made very public, very well-documented un-endorsements, and other people started doing it.

But something happened. That cascade stopped. And now you’re seeing a bit of cascading back in the other direction.

McGill: How’d that happen? And what role did Trump’s angry tweets about Paul Ryan and “disloyal Rs” play in stopping that cascade?

Zollman: Trump did something really smart—he fanned the flames of his fervent supporters in a way that made the threat to retaliate more serious. The idea was that if everybody abandoned Trump, his threat of retaliation is really an empty threat. Yes, he might attack you, but he has only so much time. You’re one among many. But if you’re one among few, he’s going to go after you.

And so Trump was really aggressive in attacking the early people who un-endorsed him, to try and signal that he had a willingness to ruin the careers of other Republicans. Trump was playing a game against the other people, precisely to make what’s called a “credible threat” in game theory.

And at the debate, he didn’t handle questions about the tape that well, but he did otherwise seem to hold his own. And I think to a lot of people’s surprise, Paul Ryan did this sort of half un-endorsement, rather than a full un-endorsement.

McGill: Where does this leave the #NeverTrump crowd—the folks who opposed him from the beginning?

Zollman: Ultimately, what you’d like to do is make it look like you’re the smart person. By refusing to endorse Trump, they’re betting he’s going to lose, and lose in a grand fashion. And after the loss, those people can say, “I saw it, I knew it was a bad idea, and that's why I never endorsed.”

Some of those people were able to do this because they were playing a game with their own constituents. They weren’t up for re-election, or they were in a constituency where the Trump supporters were a sufficiently small minority that they were not concerned about backlash.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.