Prosecutors backed away from their recommendation that former national security adviser Michael Flynn serve up to six months in prison, saying in a court filing Wednesday that probation remained a “reasonable sentence” that they would not oppose.

The filing comes as Flynn continues his effort to withdraw his guilty plea in special counsel Robert S. Mueller III’s Russia probe. Prosecutors did not explain in their filing why they reemphasized probation as a reasonable sentence for Flynn.

The shift represents the latest turn in the case in which federal prosecutors once held up Flynn as a model cooperator and suggested probation but shifted their stance to include prison time after Flynn hired a new defense team, attacked investigators and undermined the prosecution of his former business partner.

Flynn earlier accused the government of duping him into a plea agreement, but in papers filed Wednesday shifted the focus of the attack to unleash a new broadside against his former defense lawyers for allegedly concealing conflicts of interest.

In a blistering, 182-page court filing, Flynn’s new lawyers claimed that his former attorneys with prominent Washington law firm Covington & Burling “irreparably tainted” his Dec. 1, 2017, guilty plea, asserting, “Mr. Flynn’s former counsel provided nothing but ineffective and self-interested assistance of counsel to the last.”

Flynn’s new arguments increased the chances that the case of the highest-ranking Trump administration official charged — and one of the first to cooperate with Mueller’s investigation into Russian election interference — could be headed for trial instead of a Feb. 27 sentencing, legal analysts said.

Flynn, 61, admitted more than two years ago that he lied about his conversations with Russia’s ambassador and misrepresented his work for the Turkish government. He affirmed his guilt a year later under oath, after U.S. District Judge Emmet G. Sullivan questioned whether he truly accepted culpability. But new defense attorneys say that Flynn was a victim of both unscrupulous prosecutors who violated his plea agreement and an ineffective defense team “in the grip of intractable conflicts of interest.”

The dispute centers on Flynn’s admission in his original plea that he knowingly lied to the Justice Department in foreign lobbying disclosure filings about whether he and his former business partner, Bijan Rafiekian, had acted as agents for the Turkish government.

Flynn now claims that his former attorneys, Robert K. Kelner and Stephen P. Anthony, lied to him in getting him to waive concerns of a conflict of interest posed by Covington. The firm had represented Flynn in filing the Foreign Agent Registration Act forms he is accused of lying about, and Flynn’s defense claims it obscured its own errors while representing Flynn in his criminal case.

“From every angle, this case presents stunning Sixth Amendment violations of Mr. Flynn’s constitutional rights” to effective counsel, Flynn attorney Sidney Powell wrote. “He was misled, misinformed and betrayed by counsel mired in non-consentable conflicts of interests that only worsened to Mr. Flynn’s increasing prejudice.”

A spokesman for the Covington & Burling law firm said, “Under the Bar rules, we are limited in our ability to respond publicly even to allegations of this nature, absent the client’s consent or a court order.”

Kelner testified at Rafiekian’s federal trial in Alexandria last summer that Flynn reviewed and approved a filing that he has admitted contains false statements but claims he did not read.

U.S. prosecutors have until Feb. 12 to answer Flynn’s charges. Any change in plea must be approved by a judge.

Leslie McAdoo Gordon, a white-collar defense attorney in Washington and former special agent for the Pentagon’s Defense Investigative Service, said the dispute poses “a big problem” for Covington & Burling, putting into question whether Flynn’s waiver of his lawyers’ conflict was knowing and voluntary.

“Judge Sullivan has to decide whether the plea that’s already been entered was the creation not just of bad advice, but advice that falls below the standard of effective counsel,” McAdoo Gordon said.

Powell on Wednesday asked prosecutors to join her request for withdrawing Flynn’s plea, or at least to hold an evidentiary hearing at which his former lawyers might be called as witnesses to testify.