In a letter to U.S. District Judge Naomi Buchwald of the Southern District of New York filed Tuesday, government attorneys said they'd made a mistake.

The issue went back to the government's motion for summary judgment in the suit, brought by the Knight First Amendment Institute, over President Donald Trump's blocking of certain Twitter users from his official profile on the social media platform.

The suit seeks to compel the president and key members of the executive branch to unblock the users, as—according to the individuals suing along with the Knight Institute—the president's Twitter account should be held to the same standards of other government accounts and offices. Since blocking citizens from freely expressing their political views elsewhere in other government-sanctioned public forums is prohibited, Trump's Twitter feed, which he uses in his official capacity as president, should be subjected to the same standards, they argue.

The government's argument is founded on the premise that the courts lack the authority to compel the president to do this, and a whole range of things. To back this up, the government attorneys cited a host of prior cases they say backed them up. This included National Association of Internal Revenue Employees v. Nixon, a case from the Nixon era out of the Washington, D.C., district court.

The only problem, the attorneys acknowledged on Tuesday, is that specific case actually was reversed on appeal.

The district court ruled against the federal employees union, which sought to force President Richard Nixon to follow federal rules related to statutory pay increases. The plaintiffs argued that the decision wasn't a discretionary one, and that the court should make the president perform his “ministerial” duties.

While the lower court found it did not have jurisdiction over the president, on appeal, the appellate court disagreed, as the Justice Department noted in its letter. The panel in its 1974 decision found that the president “had a ministerial, non-discretionary duty to act, and that the court could enter equitable relief with respect to such a ministerial duty,” according to the DOJ's letter to Buchwald.

This fact has not been lost on the Knight Institute, which itself cited the appellate court's decision in its own papers as proof courts have the power to act to force the president to follow the law.

Which is, of course, just what the court will be asked to do Thursday by the plaintiffs during oral arguments on the cross-motions for summary judgment in the suit.

“We look forward to convincing the court of its authority at the hearing tomorrow,” Carrie DeCell, a staff attorney with the Knight Institute, said.

A spokesperson for the DOJ did not respond to a request for comment.