Donald Trump’s Twitter account now has 40 million followers. It ranks 21st worldwide among 281.3 million or so accounts. It’s no secret that Trump is proud of his ability to use the account to communicate directly with his constituents. This summer, the president tweeted, “My use of social media is not Presidential—it’s MODERN DAY PRESIDENTIAL.” He meant that his tweets are official statements of the president of the United States. The National Archives concurs: It says they must be preserved under the Presidential Records Act. When Trump’s aides have tweeted about the president’s agenda, they have referred to it as the agenda of @realDonaldTrump.

Trump has used Twitter to announce his plan to ban transgender people from the military, to blow air kisses to Russia’s Vladimir Putin, to attack the so-called fake media’s coverage of his administration, and to assert his version of the facts (“No WH chaos!”). Almost every week, he takes to Twitter to feud with new foes: NFL players, for kneeling during the national anthem; the mayor of San Juan, Puerto Rico, for deriding the federal government’s sluggish response to the island’s dire needs after the monstrous Hurricane Maria; Senator Bob Corker of Tennessee, for tweeting, “It's a shame the White House has become an adult day care center.” Trump’s following climbs about 80,000 a day—a rate of almost 30 million add-ons a year.

Anyone with a Twitter account can follow the president.

Well, almost anyone.

In June, Rebecca Buckwalter-Poza, a writer and legal analyst in Washington, DC, was blocked from reading and replying to the president’s account and from reading other related comments. This happened after Trump tweeted, “Sorry folks, but if I would have relied on the Fake News of CNN, NBC, ABC, CBS washpost or nytimes, I would have had ZERO chance winning WH,” and Buckwalter-Poza tweeted back, “To be fair you didn’t win the WH: Russia won it for you.” Also in June, a police officer in Houston, Texas, named Brandon Neely was similarly blocked after the president tweeted, “Congratulations! First new Coal Mine of Trump Era Opens in Pennsylvania,” and Neely replied, “Congrats and now black lung won’t be covered under #TrumpCare.” Many other people have been blocked, apparently for similar dissents.

It raises the question: Are social media platforms like Twitter subject to the First Amendment? Is there a right to free speech on social media owned by private corporations?

The Knight First Amendment Institute thinks so. In July, the institute sued the president, his director of social media, and his press secretary to unblock the blocked. By banning these users based on views they expressed about tweets by the president, the Institute argues, Trump violated the users’ right to free speech because the blocks were based on disagreement with the users’ messages. (I am affiliated with the institute, but not directly involved in the lawsuit.) Two weeks ago, as part of this litigation, lawyers for the president acknowledged that he personally blocked the Twitter users “because the Individual Plaintiffs posted tweets that criticized the president or his policies”—what free speech law calls “viewpoint discrimination.” In places where the First Amendment applies—such as public forums—it bars the government or its officials from such bias.

The president’s Twitter account is not a traditional public forum, like a town hall or public park, where citizens are said to exchange views in the “marketplace of ideas” on which, it’s also said, democracy depends. In those forums, the government can restrict speech based on its content only if the restriction serves a strong interest of the government, like preventing violence. But here’s the thing: In an age when so much public discourse happens on platforms like Twitter, @realDonaldTrump should be subject to the same strict standard as a designated, or limited, public forum used for expressing views of the president.