The last-minute settlement of Dominion Voting Systems’ lawsuit against Fox News defused a high-stakes test of the First Amendment protections afforded to the media. But more challenges are likely on the horizon.

Nearly 60 years after the Supreme Court’s unanimous decision in New York Times v. Sullivan, which made it harder for public figures to win libel cases against the media, the landmark ruling is under sustained assault from judges, politicians and lawyers, most but not all of them conservatives.

The Dominion lawsuit, in which the voting machine company sought $1.6 billion in damages from Fox News for spreading falsehoods about Dominion’s role in the 2020 elections, had the potential to reshape the debate.

If Fox News lost, a powerful news organization faced the prospect of record-breaking damages. But a victory for the cable news network would have raised questions — even among lawyers who represent the news media — about whether federal courts’ interpretations of the First Amendment made it impossible to hold anyone accountable for reckless and damaging lies.

It’s not a coincidence that a founder of one of the law firms that represented Dominion is leading a campaign to get the Supreme Court to overturn its decision in Sullivan.

The agreement by Fox News to settle for $787.5 million — among the largest payouts ever in a defamation lawsuit — means that the scope of the Sullivan ruling will not be tested this time.

In that 1964 decision, the justices ruled that to win a libel suit, public officials had to do more than show that factual inaccuracies in an article harmed them. They also had to prove that those falsehoods were the product of “actual malice” — in other words, they were intentional or caused by a reckless disregard for the truth.

For decades, the Sullivan ruling was widely regarded as an essential safeguard that allowed journalists to aggressively cover public figures without fear that accidentally publishing an error — even a serious one — could expose them to devastating damages.

But over the past several years, with former President Donald J. Trump and other conservative leaders bashing the news media, that consensus has frayed.

A turning point came in 2019 when the Supreme Court decided not to hear a case in which a woman who had accused Bill Cosby of rape sued him for defamation. Justice Clarence Thomas, who agreed that the court shouldn’t accept the case, wrote that the Sullivan decision and some of the court’s subsequent rulings “were policy-driven decisions masquerading as constitutional law” and should be overturned.

Justice Thomas’s fiery concurrence accelerated a campaign to chip away at First Amendment protections for the news media. Two years later, Justice Neil M. Gorsuch also signaled his openness to reconsidering Sullivan, which he said had “evolved into an ironclad subsidy for the publication of falsehoods by means and on a scale previously unimaginable.”

In recent court cases, Republican politicians suing the news media for defamation — including the former Senate candidates Don Blankenship and Roy Moore and the former congressman Devin Nunes — have explicitly pushed judges to abandon the Sullivan ruling.

Aside from trying to win their cases, the apparent goal was to present the Supreme Court with a vehicle to reconsider Sullivan.

“That is definitely the strategy,” said Lee Levine, a prominent First Amendment lawyer who, until his retirement, regularly represented The New York Times and other news organizations. “It will continue.”

At the same time, conservative groups like the Heritage Foundation and the Federalist Society have been convening public panels to discuss how the Sullivan ruling supposedly permitted biased, vindictive journalists to defame their enemies with impunity.

Elizabeth M. Locke, a founding partner at Clare Locke, a defamation law firm that represented Dominion in its lawsuit against Fox News, has emerged as one of the most vocal advocates for overturning the Sullivan ruling.

“It’s virtually impossible to bring and win one of these cases,” Ms. Locke said this year. The media “have complete immunity from liability.” (In fact, Ms. Locke’s law firm and others have recently secured multimillion-dollar jury verdicts for public figures suing the media for defamation.)

Ms. Locke was speaking at a televised event that Gov. Ron DeSantis of Florida hosted to build support for reversing Sullivan.

“It would contribute to an increase in the ethics in the media and everything if they knew: You know what? You smear somebody, you know it’s false and you didn’t do your homework, you’re going to have to be held accountable for that,” Mr. DeSantis said at the February event, the phrase “SPEAK TRUTH” emblazoned on a screen behind him. (In fact, the Sullivan ruling does not shield journalists from liability if they know what they are publishing is false.)

Mr. DeSantis has pushed the State Legislature to curtail legal protections for the media, which some experts regard as an attempt to trigger litigation that would give the Supreme Court an opportunity to reconsider Sullivan.

The enormous Dominion settlement undercut the arguments made by Ms. Locke, Mr. DeSantis and others that libel cases are essentially unwinnable for public figures.

“This is an example of how plaintiffs can win — and win big — under the actual malice standard,” said Rodney A. Smolla, one of the lawyers representing Dominion alongside Ms. Locke’s firm. “This takes some of the oxygen out of that argument” that libel cases are unwinnable.

But, he said, the reason the settlement was so large was that Dominion’s lawyers had used the legal discovery process to unearth troves of records in which Fox executives and on-air personalities privately acknowledged that the allegations they were peddling about Dominion were false.

Mr. Smolla, who is president of the Vermont Law and Graduate School, said this showed that judges in defamation cases should more frequently allow plaintiffs to proceed to discovery before they were required to persuade the court that defendants may have acted with actual malice.

“The fact that the court here gave Dominion the opportunity to engage in discovery paved the way for the victory,” he said. “This case is the ultimate example of that — it’s really hard to make an actual malice case without discovery.”

It is unclear whether the Dominion settlement will sway Justice Thomas or Justice Gorsuch. Justice Thomas’s argument for overturning Sullivan was largely based on his claim — which some legal scholars dispute — that there was no historical rationale for the court’s actual malice standard. Justice Gorsuch was more focused on the practical implications of the standard.

For her part, Ms. Locke viewed the outcome of the Dominion lawsuit as validation of her belief that the news media needed to be reined in.

“The size of the Dominion settlement shows just how comfortable the American media has become lying to the public under the Sullivan regime,” she wrote in an email on Wednesday. “There are endless other examples that go unaddressed every day.”

In light of the Dominion settlement, did she still think the Supreme Court should reverse Sullivan?

Ms. Locke responded, “Unequivocally yes.”