U.S. District Judge Naomi Reice Buchwald of the Southern District of New York has asked Justice Department attorneys to say how, exactly, President Donald Trump's personal Twitter account differs from official accounts such as @POTUS and @WhiteHouse.

In a letter to the government's attorneys Tuesday, Buchwald referred back to oral arguments held March 8 on summary judgment motions filed by both sides in Knight First Amendment Institute v. Trump. During the hearing, Buchwald's questioning centered on Trump's use of Twitter—which he famously has used in part to convey administration messages.

In the case, free-speech advocates are arguing that Trump may not block users from access to his personal Twitter account, @realDonaldTrump, the same way elected officials are unable to restrict political speech in other public forums. Buchwald was searching for a way to guarantee free-speech rights in a case where a public official uses a private account to communicate statements of official policy.

At one point, Buchwald brought up an alternative to blocking, questioning whether Trump could just “mute[] the person that he finds personally offensive,” rather than blocking them.

Buchwald did observe that not “every tweet on the account could be considered an official statement of government position.” Where then, she asked, could an appropriate line be drawn?

In her letter Tuesday, Buchwald noted that, during arguments, the government had agreed that were users to be blocked from so-called official accounts, it was “probably true that the government cannot block individuals purely on the basis of viewpoint from a government account like the @POTUS account.”

Buchwald said the court “neglected … to address the impact of this position on the question currently before” it: “whether such blocking may occur on the @RealDonaldTrump account.”

“If the government continues to take the position that users may not be blocked from the @POTUS and @WhiteHouse accounts, it should explain all of the ways in which the First Amendment analysis differs for those two accounts on the one hand and the @RealDonaldTrump account on the other,” Buchwald wrote. “If the government no longer takes the position that such blocking is unconstitutional, it should explain why such blocking is in fact permissible.”

The judge set a March 28 deadline for the government to reply, and seven-day response deadline for the plaintiffs after the government's letter.

“We're glad the judge asked this question,” said Katie Fallow, senior staff attorney at the Knight First Amendment institute at Columbia University, in an emailed message. “It's hard to understand the government's apparent position that the First Amendment would bar the president from blocking critics from the @POTUS account, but not from @realDonaldTrump—the account he uses almost daily to introduce new policies, announce nominations to key government posts, and otherwise convey important news and information about the administration.”

A spokeswoman for the DOJ declined to comment.