A U.S. judge will preside over a climactic confrontation in Washington at 11 a.m. Tuesday over the Justice Department’s bid to dismiss the criminal case against Michael Flynn, the former Trump national security adviser who pleaded guilty to lying to federal investigators.

In a case likely to define the limits of executive- and judicial-branch powers, U.S. District Judge Emmet G. Sullivan set final arguments after an appeals court affirmed his authority to scrutinize Attorney General William P. Barr’s controversial request to toss the prosecution of the highest-ranking Trump adviser charged in special counsel Robert S. Mueller III’s Russia investigation.

The full U.S. Court of Appeals for the D.C. Circuit directed Sullivan in an 8-to-2 order to act “with appropriate dispatch.” Tuesday’s publicly teleconferenced hearing promises to provide high legal and politicaldrama five weeks before an election in which Flynn’s contentious prosecution has electrified President Trump’s supporters and opponents.

Flynn, 61, has been awaiting sentencing since pleading guilty in December 2017 to lying about his contacts with Russia’s ambassador after Moscow intervened to support Trump in the 2016 U.S. election.

Trump and his allies have made the former three-star Army general’s cause a focus of efforts to discredit the criminal inquiry into whether individuals associated with Trump’s campaign cooperated with Russia’s illegal assistance. The efforts include a string of government disclosures that have drawn fresh scrutiny to the judgment of FBI agents and Mueller prosecutors but have not undercut findings that the FBI had a legal basis to open the wider investigation and acted without political bias.

The Justice Department in May moved to drop Flynn’s guilty plea to lying about his pre-inauguration contacts with then-Ambassador Sergey Kislyak, in which Flynn asked that Moscow not respond to U.S. sanctions until Trump took office. The department based the reversal on Barr’s conclusion from a review he ordered that Flynn’s interview by the FBI “was unjustified by the counterintelligence investigation into [him]” and so his lies were immaterial to any crime.

Law enforcement officials and Democratic critics condemned the turnabout, accusing Barr of undermining the department and protecting the president, citing the drive to exonerate Flynn and soften the sentencing of Trump friend Roger Stone for lying to investigators in a House Russia probe. They also point to efforts to facilitate the early prison release of former Trump campaign chairman Paul Manafort. convicted of crimes stemming from his lobbying for a pro-Russian politician in Ukraine.

Tuesday’s hearing will turn on a federal rule prescribed by the Supreme Court in 1944 that requires U.S. prosecutors to obtain “leave of court” — or permission from a judge — before dismissing a prosecution. Sullivan, the longest-serving active federal judge on the district court in Washington and a judicial nominee of presidents of both parties, appointed former New York federal judge John Gleeson to argue against the government to preserve an adversarial proceeding.

A swift ruling is expected, whatever the outcome. Flynn’s attorneys claim the judge has engaged in a “flagrant personal and partisan assault” against him. The Justice Department asserts the executive branch has sole power to dismiss cases. Gleeson argues the Supreme Court intended for the judicial branch to weigh whether dismissal is in the public’s interest before approving corrupt or politically motivated requests.

Flynn pleaded guilty to lying in an FBI interview on Jan. 24, 2017, to conceal conversations with Kislyak. Flynn repeated the lie to White House staffers and Vice President Pence, leading to the firing of Trump’s first national security adviser three weeks later.

Flynn cooperated with the Mueller probe, and leniency was initially recommended at sentencing. But he switched course after Mueller’s investigation, accusing prosecutors and his former defense attorneys of concealing FBI misconduct and coercing him into pleading guilty.

The department rejected those claims through last year, and Sullivan ruled Flynn was relying on bogus theories to deny Mueller’s central finding of Russian interference and to wriggle out of his repeated sworn admissions of misconduct.

“The sworn statements of Mr. Flynn and his former counsel belie his new claims of innocence and his new assertions that he was pressured into pleading guilty to making materially false statements to the FBI,” Sullivan wrote in December.

But at Barr’s direction, the Justice Department launched a review of the case in January. In moving to dismiss Flynn’s conviction on May 7, it cited “frail and shifting justifications for its ongoing probe,” the FBI’s irregular moves to question him and earlier abuses in surveillance applications.

The department cited recently uncovered FBI records including communications showing the bureau had decided to close a counterintelligence investigation of Flynn — dubbed Operation Razor — before learning of his December 2016 calls with Kislyak. The Justice Department also said that the FBI knew from transcripts that the calls probably did not give rise to a crime by themselves and that FBI officials differed over how to handle or interpret his actions.

In response, more than 1,100 former prosecutors said in a friend-of-the-court brief that the Justice Department distorted facts and appeared to have been bent to serve the president’s will.

Gleeson urged Sullivan to deny the dismissal motion, calling it “a gross abuse of prosecutorial power.”

“The Government has engaged in highly irregular conduct to benefit a political ally of the President,” Gleeson summarized, saying, “There is clear evidence . . . [that it] reflects a corrupt and politically motivated favor unworthy of our justice system.”

Gleeson argued the FBI had ample, legitimate grounds to investigate Flynn’s lies, which went to the heart of the investigation of whether Trump’s campaign coordinated with Russia’s intervention in the election, whether Flynn was seeking to reward Russia at Trump’s direction or others’, and whether his lies exposed Flynn to Russian blackmail.

Flynn faces a sentence of zero to six months under his initial plea deal. Flynn’s initial defense team postponed a December 2018 sentencing hearing after Sullivan balked at a recommendation of probation. At one point, Sullivan summarized Flynn’s lies to the FBI and to the White House and about his lobbying work for Turkey by saying, “Arguably, you sold your country out.”

Flynn hired new attorneys in June 2019, led by former federal prosecutor Sidney Powell, who called Sullivan’s actions in the case unconstitutional. She argued that the “Executive Branch has exclusive authority and absolute discretion to decide whether to prosecute a case.”

The Justice Department agreed. Acting solicitor general Jeffrey B. Wall called Sullivan’s inquiry impermissible, arguing to the D.C. Circuit that it “would usurp the core executive power to decide whether to continue a prosecution.”