If the last two elections were a renaissance for data-driven journalism, turning statistician Nate Silver into a household name, the current presidential cycle seems like a return to the Dark Ages. After years in which we grew accustomed to thinking of polling as more science than art, Donald Trump’s spectacular rise to the top of the G.O.P. field turned the entire world of political punditry on its head. How did everyone, Silver included, fail to predict the possibility that a candidate initially written off as a joke (and a racist, to boot) might find himself a stone’s throw away from either triggering a historic contested convention or winning the Republican nomination outright?

One reason, Silver suggests, is that Trump represents a “black swan”—a concept developed by risk analyst Nassim Taleb to describe incredibly rare, hard-to-predict events, like the 9/11 attacks, that have an outsize impact. “To be fair, we were more skeptical than the average—we weren’t saying it was [a] zero” percent chance, Silver, the editor in chief of FiveThirtyEight, told Peter Kafka in a recent Re/Code podcast. But “if you’re going to have a 2 percent, 5 percent probability come through, it better look pretty weird.”

Silver, a statistician by trade and an early proponent of sabermetrics in baseball, was looked to as a presidential soothsayer after he correctly predicted the outcome of the 2012 presidential election in the electoral college, state by state. Like most everyone else, he dismissed Trump’s chances back in 2015, sticking to his predictions even as the lurid orange spoiler climbed higher and higher in the polls. Silver has since admitted he misjudged the extent of the billionaire’s populist appeal—although, he argued, Trump’s candidacy could just as easily have failed to reach escape velocity if a few more states hadn’t broken his way, or if the media hadn’t covered him so much.

“But instead, we are seeing the Republican party on the verge of falling apart,” he told Kafka. “I know those are strong words, but to have a nominee who is at odds with every institution that had power in the party before, I just—you know—there’s almost no recent precedent for it in American history, and I don’t know enough pre-World War II history to say if there was a distant precedent for it, but that is pretty substantial.”

If Trump can secure the nomination, Silver now believes Trump has a 25 to 30 percent chance of winning the general election—a possibility he acknowledges was difficult at first for him to recognize. “I guess one reason I kind of thought, well, this is very unlikely to happen, because if it happens, it’s going to be so incredibly consequential,” said Silver. “And now that it’s happening, it’s incredibly consequential for the Republican Party.”