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.