Mr. Carusone said that Mr. Hannity’s evolution was goaded by Mr. Trump’s ability to use social media to promote unproven, reckless arguments — and by social media companies’ ability to give him a platform without themselves facing repercussions for his speech, thanks to Section 230. “Trump increasingly was able to leapfrog Fox News, in terms of building a relationship to Fox News’s own audience,” he said. “So Fox News lost the keys to the gate.”

But in the past month, Mr. Trump has lost his set of keys, too. He was kicked off Twitter and Facebook after the Capitol riot, and since leaving the White House he has been as quiet as a church mouse. In his absence, Fox News has begun to focus more on attacking Mr. Biden and other Democrats on the news of the day than on importing conspiracy theories from online.

Going forward, Mr. Carusone said, “I think they’ll try to soften some of the content on the edges, and to lean heavier into the partisan attacks and less on the right-wing fever swamp fantasies and narratives.”

Proponents of media reform say that this moment presents a once-in-a-generation opportunity to rethink government policy related to online speech in particular. Ellen Goodman, a Rutgers Law School professor who focuses on information policy, said that maintaining a healthy marketplace of ideas was crucial to democracy.

“If this is a moment of radical, ‘Build Back Better’ adjustments, and a revival of the middle class, what would the democracy-building part of that look like?” she said. She proposed instituting taxes or regulations that would “make the surveillance-capitalism model less attractive,” preventing social media companies from microtargeting audiences in the interest of selling them products.

Jonathan Zittrain, a Harvard Law School professor who studies digital media, sees a sea change coming. In the early decades of the internet, he said, most legal discussions were guided by a question of “rights,” particularly the right to free speech under the First Amendment. But in recent years, a new interest in what he called “the public health framework” has taken hold.

“Misinformation and extremism — particularly extremism that’s tied to violence — can result in harm,” Mr. Zittrain said. “Given that there are compelling things in both the rights framework and the health framework, there’s going to be a balance struck.”