A federal judge on Wednesday appointed Debevoise & Plimpton partner John Gleeson to oppose the Justice Department's move to dismiss the prosecution of Michael Flynn, the former Trump national security adviser who twice pleaded guilty to lying to investigators about his past communications with the Russian ambassador to the U.S.

U.S. District Judge Emmet Sullivan selected Gleeson a day after signaling his interest in hearing outside views on the Justice Department's sudden abandonment of the Flynn case, a move that renewed criticism that U.S. Attorney General William Barr was intentionally trying to undermine the special counsel's Russia investigation and to interfere to protect an ally to President Donald Trump.

Gleeson, a former federal judge in Brooklyn, was among Barr's critics. Just days ago, he co-authored an op-ed in The Washington Post noting that Sullivan could reject the Justice Department's motion to dismiss the Flynn case and hand down a sentence.

"Flynn's guilt has already been adjudicated," Gleeson wrote in the op-ed with fellow Debevoise partner David O'Neil and Marshall Miller, both former high-ranking Justice Department officials. "So if the court finds dismissal would result in a miscarriage of justice, it can deny the motion, refuse to permit withdrawal of the guilty plea and proceed to sentencing."

Sullivan tasked Gleeson with advising the court whether it "should issue an order to show cause why Mr. Flynn should not be held in criminal contempt for perjury" pursuant to a federal law that gives judges broad authority to punish "misbehavior of any person in its presence or so near thereto as to obstruct the administration of justice."

Flynn's defense team is opposed to allowing outside voices, or amicus curiae, to weigh in on the dismissal, arguing no friend-of-the-court had a place in the high-profile prosecution.

"No further delay should be tolerated or any further expense caused to him and his defense," Flynn's defense lawyers wrote in a brief filed Tuesday. The defense lawyers have urged Sullivan to "immediately" grant the Justice Department's request to dismiss the case.

Barr has refuted broad criticism that he was acting out of bounds when his office stepped in to bring an abrupt end to Flynn's case. Earlier this year, Barr had appointed Jeffrey Jensen, the top federal prosecutor in St. Louis, to scrutinize the case. Barr has said the move to dismiss Flynn's case was made at Jensen's recommendation.

Flynn resigned as Trump's national security adviser within weeks of the inauguration amid questions about whether he misled Vice President Mike Pence about his communications during the transition with Sergey Kislyak, then Russia's ambassador to the United States.

Flynn pleaded guilty in 2017 and agreed to cooperate with Robert Mueller III, the special counsel leading the Russia investigation. He apologized in open court for his action.

Flynn had been awaiting sentencing and faced anywhere from probation to six months in prison. In January, represented by new defense counsel, Flynn moved to withdraw his guilty plea. That effort had been pending at the time U.S. Attorney Timothy Shea filed papers asking Sullivan to dismiss the Flynn case with prejudice.

Barr's Justice Department now contends the FBI did not have sufficient grounds to interview Flynn in the first place, an argument that other Justice Department officials contest. A lead prosecutor on the Flynn case, Brandon Van Grack, withdrew from the prosecution shortly before Shea asked Sullivan to dismiss the case. Shea's was on the only name on the motion.

Sullivan said earlier this week he would set a briefing schedule for the filing of any friend-of-the-court briefs. The move effectively slowed down the Justice Department's effort to abandon the prosecution.