WASHINGTON, D.C. — President Donald Trump threatened Wednesday to strongly regulate or close down social media platforms he deems unfriendly to conservatives, escalating a war with Silicon Valley a day after Twitter for the first time warned that Trump was posting false claims, about mail-in voting.

Trump’s attacks came as Twitter faced competing pressures from liberals, some of whom want Trump banned from his favorite platform for deliberately spreading misinformation, and from Trump supporters who say social media companies discriminate against them.

Trump’s threat to muzzle a private company as retaliation for its corporate policy marks another shattering of traditional norms in the White House, especially for Republicans who generally oppose regulation.

Yet like many of Trump’s threats on Twitter and elsewhere, this one appears mostly about political posturing. It comes as the U.S. death toll from COVID-19 is likely to pass 100,000, or more than the total number of Americans killed in both the Vietnam and Korean wars.

The First Amendment bars the government from restricting speech, but it does not prohibit private companies from imposing restrictions.

And unlike television stations and networks that rely on government-issued broadcast licenses, the internet lacks a so-called fairness doctrine, a loosely enforced requirement that promotes ideological balance.

Trump has more than 80 million followers on Twitter and has used his reach to dominate the news cycle and public discourse since he entered politics, making his threat to shutter the platform even more unlikely.

But Trump enjoys a headline-grabbing fight, even with those most helpful to him. He has lambasted Fox News, former members of his administration and senior Republican lawmakers at times, either out of anger or to keep them in line.

Fittingly, the president’s threats against Twitter were delivered on the platform itself, in a series of morning tweets.

“Twitter has now shown that everything we have been saying about them (and their other compatriots) is correct. Big action to follow!” he wrote.

The latest skirmish came after Twitter began adding informational links to Trump’s unfounded tweets that mail-in voting will lead to widespread election fraud.

Twitter did not intervene after Trump sent a series of more explosive tweets that accused cable TV host Joe Scarborough of killing an intern decades ago, a baseless conspiracy theory that found root in the White House.

The Wall Street Journal editorial board, which often aligns with Trump on policy, urged him to stop, writing Wednesday that he is “debasing his office, and he’s hurting the country” with the Scarborough tweets.

Nikolas Guggenberger, executive director of the Information Society Project at Yale Law School, said Trump’s behavior is a challenge for social media companies, because they depend on him for content and attention.

“President Trump is not only president, but he is one of the most successful influencers,” Guggenberger said. “He’s not only a government entity that can regulate them, but a significant contributor to their business model.”

Guggenberger rejects conservative claims that Twitter and other social media companies discriminate against the right, and finds Trump’s attempts at coercion more troubling.

“It’s one thing to try to regulate speech in an abstract manner,” he said. “It’s a completely different thing to try to rein in speech when it concerns you.”

The Communications Decency Act, passed in 1996 by Congress in its first attempt to regulate the burgeoning internet, determined that internet service providers are not responsible for the content posted by third-party users.

Provisions in the law have “given rise to pretty much unfettered content on social media,” said Roy Gutterman, director of the Tully Center for Free Speech at Syracuse University’s Newhouse School of Public Communications.

Despite a lack of government oversight and legal liability, Twitter and other tech behemoths remain increasingly susceptible to public pressure —often, propelled by their own platforms—to take more responsibility when it comes to regulating content.

“We’re in uncharted areas now and in a position where things are so outrageous —outrageous information, outrageous tweets, outrageous messages might require bolder responses,” Gutterman continued, although he expects Twitter and other companies to leave the bulk of the regulation of questionable content to their users.

While few conservatives have defended Trump’s tweets about Scarborough, more have rallied to his fight with Twitter. A Pew survey taken in 2018 found that 64% of Republicans believe technology companies support the views of liberals over conservatives.

Many on Twitter on Wednesday pointed to tweets from Yael Roth, the head of site integrity for Twitter, that disparaged Trump supporters and “THE ACTUAL NAZIS IN THE WHITE HOUSE,” among other explosive charges. Roth does not appear to be involved in enforcing the company’s rules on civility and is instead focused on protecting it from malign attacks.

Kellyanne Conway, the president’s counselor, appeared to encourage harassment of Roth during an interview on “Fox & Friends.”

“Somebody in San Francisco will wake him up and tell him he’s about to get a lot more followers,” she said after spelling his name out on the air.

Charlie Sykes, a former conservative talk radio host who has become a Trump critic, believes there is little Twitter can do to Trump that would not backfire.

Banning him would make the president a martyr, his favorite place in the political universe. And even if Trump were kept off Twitter, he would not lose his ability to command an audience.

“Trump is the bully pulpit,” Sykes said. “The source of the malignancy is Trump himself.”

That has not contained outrage on the left.

Jesse Lehrich, a former spokesman for Hillary Clinton, announced that he was teaming with Nicole Gill, another liberal activist, to form Accountable Tech, an advocacy group aimed at pressuring tech companies to fight “the proliferation of online misinformation, deception, and manipulation.”