And while making the case for Trump during oral arguments before a three-judge panel, Justice Department attorney Jennifer Utrecht disclosed that the president — on his own — is wholly responsible for blocking users with the Twitter account.

A federal judge ruled last May that Trump could not block people on Twitter because it violates their First Amendment Rights. US District Judge Naomi Reice Buchwald wrote at the time that the president's Twitter account constituted what the Supreme Court considered to be a "public forum."

"The blocking of the plaintiffs based on their political speech constitutes viewpoint discrimination that violates the First Amendment," Buchwald said in her decision.

The lawsuit was originally filed in 2017 in the Southern District of New York by the Knight First Amendment Institute at Columbia University and seven people who were blocked by the president. Plaintiffs included a physician in California, a comedy writer in New York, and a police officer in Texas.

The federal government appealed Buchwald's ruling, arguing that the president's Twitter account was a personal, rather than a government, account.

Katie Fallow, a senior staff attorney at the Knight First Amendment Institute, said that the involved plaintiffs have expressed shock that the president personally went out of his way to block them.

While the government's attorney acknowledged in yesterday's arguments that the president does operate his Twitter as an official account, she said that he blocks people as a private person and on his own personal whim.

"They don't want to concede that it's a public forum, and the reason why is because the first amendment only applies to actions by the government. It doesn't apply to actions by individual persons," Fallow said. "And so what they're doing in trying to avoid the consequences of this lawsuit is to say 'oh, when he blocked people, that was just purely a personal decision.' "

When a user blocks a person on Twitter, that blocked person can't view or reply to the user's Tweets — which the Knight Institute has argued violates their constitutional rights since they can no longer engage with or reply to the president. It could also set a dangerous precedent if public officials have the ability to block their critics whenever they voice dissenting opinions online, and may present a lopsided view of public opinion in the comment threads of those social media posts.

Trump often uses Twitter as a way to attack the media and political adversaries. He currently has more than 59 million followers on the platform.

During Tuesday's hearing, one of the judges brought up recent tweets by Trump, including one that recognized Israel's sovereignty over the Golan Heights territory and another that announced his nomination of Stephen Moore to the Federal Reserve Board, and questioned Utrecht on whether she considered those to be official actions. While she said they were, she added that the president blocks in a personal capacity and created the account before he became president.

Earlier this year, The US Court of Appeals for the Fourth Circuit decided that a county official in Virginia who blocked a critic from her Facebook page did violate the First Amendment. Judge James Wynn Jr. described the official's attempt to block the person as "unconstitutional viewpoint discrimination," according to the opinion of the case.

Now, the federal judges in Manhattan must decide on a similar scenario when it comes to the president. Fallow said that not only is it problematic that Trump is trying to bar people from viewing the content he posts online, but it could open the floodgates for public officials at every level of government nationwide to block their critics from speaking out online.

"We have these very strong cases and principles protecting free speech by journalists, by ordinary citizens, and particularly for criticism of public officials, even criticism that is extremely pointed or even very offensive," Fallow said. "And now, increasingly, public officials have turned to social media as the primary place where they are talking to and hearing from constituents, and it's our view that the First Amendment should apply equally to these new kinds of virtual town halls."