A retired federal judge accused the Justice Department on Friday of yielding to a pressure campaign led by President Trump in its bid to dismiss the prosecution of former national security adviser Michael Flynn for lying to federal investigators.

In a 30-page court filing in Washington, former New York federal judge John Gleeson called Attorney General William P. Barr’s request to drop Flynn’s case a “corrupt and politically motivated favor unworthy of our justice system.”

“In the United States, Presidents do not orchestrate pressure campaigns to get the Justice Department to drop charges against defendants who have pleaded guilty — twice, before two different judges — and whose guilt is obvious,” said Gleeson, who was appointed by the court to argue against the government’s request to dismiss the case.

Gleeson’s filing set the stage for a potentially dramatic courtroom confrontation Sept. 29 with the Justice Department and Flynn’s defense over the fate of the highest-ranking Trump adviser to plead guilty in special counsel Robert S. Mueller III’s Russia investigation. Friday’s filings echo earlier arguments from Gleeson, who called the Justice Department’s attempt to undo Flynn’s conviction a politically motivated and “a gross abuse of prosecutorial power.”

U.S. District Judge Emmet G. Sullivan of the District of Columbia set the hearing date after a federal appeals court upheld his authority to review and rule on the government’s dismissal request on Aug. 31. The hearing before Sullivan was selected from three dates proposed by the parties and is scheduled the same day as the first presidential debate between Trump and Democratic nominee Joe Biden.

Flynn’s lawyer Sidney Powell on Friday called Gleeson’s filing “predictable and meaningless,” saying again that Flynn’s investigation was “corrupt from its inception.”

The Justice Department has argued that the executive branch has sole constitutional authority over prosecutorial decisions and that courts cannot “look behind” its decision-making or motives.

Flynn, 61, awaits sentencing after pleading guilty in December 2017 to lying in an FBI interview on Jan. 24 that year to conceal conversations during the presidential transition with Sergey Kislyak, then the Russian ambassador to the United States. The conversations related to securing potential relief from U.S. sanctions once Trump took office.

Flynn repeated the lie to White House staff and Vice President Pence, leading to the firing of Trump’s first national security adviser three weeks later.

Although Flynn cooperated with the Mueller probe and was prepared to be sentenced December 2018, he switched course after Mueller’s investigation ended and Barr took office last year. Flynn then accused prosecutors and his former attorneys of coercing him into pleading guilty and concealing FBI misconduct, claims that the department and Sullivan rejected.

At Barr’s direction and after a fresh review, however, the Justice Department in May reversed itself and moved to end Flynn’s prosecution, concluding that FBI agents did not have a valid reason to question the retired Army three-star general, so any lies he told did not amount to a crime.

Trump and his allies have also stepped up attacks against what the president has called an unfounded criminal investigation into whether individuals associated with his campaign conspired in Russia’s effort to interfere in the 2016 U.S. election. Trump has said he is “strongly considering” pardoning Flynn, who the president said was a victim of “dirty, filthy cops at the top of the FBI.”

Before ruling on the government’s request, Sullivan appointed Gleeson to advise the court by arguing against the department, since the government was no longer taking an adversarial position against the defendant.

Flynn’s attorneys had asked the U.S. Court of Appeals for the D.C. Circuit to order Sullivan to immediately drop the case and bar Gleeson from participating in any hearing, accusing both of bias. Flynn initially prevailed before a split three-judge panel before the full court ruled 8 to 2 against him, finding intervention by the appeals court was premature.

Flynn’s defense has not said whether it plans to ask the Supreme Court to intervene.

The Justice Department’s reversal in Flynn’s case has prompted intense criticism, including from law enforcement officials and Democrats, who said the department had given in to political pressure.

A bipartisan Senate Intelligence Committee investigation into Russian election interference last month found that Flynn and Kislyak’s communications about sanctions were relevant to assessing what the Russian government sought to gain from the president-elect “and the counterintelligence vulnerabilities associated with the Transition.” Flynn discussed his Kislyak contacts with other senior Trump officials before lying to Pence and others about their subject matter.

“Pursuant to an active investigation into whether President Trump’s campaign officials coordinated activities with the Government of Russia, one of those officials lied to the FBI about coordinating activities with the Government of Russia,” Gleeson said earlier in the case.

“That is about as straightforward a case of materiality as a prosecutor, court, or jury will ever see,” he wrote.