A federal judge agreed Tuesday to postpone Michael Flynn's sentencing after a hearing to decide the punishment for President Donald Trump's former national security adviser went awry.

The surprise development came after Judge Emmet Sullivan in Washington, D.C., offered to give Flynn, a retired lieutenant general, more time to consider his decision to plead guilty to lying to investigators probing Russia's interference in the 2016 election. Sullivan described the offense as “serious” and said he could not guarantee a sentence without prison time, even after the special counsel's office recommended that Flynn not be incarcerated.

After a brief recess, Covington & Burling partner Robert Kelner said Flynn was “prepared to take your honor up on the suggestion of delaying sentencing.” The delay, Kelner said, would allow Flynn to “eke out the last modicum of cooperation” in his deal to assist in a separate case being prosecuted in Alexandria, Virginia, involving two of Flynn's former business associates.

Kelner envisioned that Flynn could be called to testify in a case against Bijan Rafiekian and Kamil Ekim Alptekin, who were charged Monday with acting as unregistered agents of the Turkish government and lying to the FBI.

Sullivan set a March 13 deadline for a status report.

The surprise development came after what began as a routine sentencing hearing devolved into a dramatic discussion on Flynn's conduct. Sullivan at one point questioned whether, “hypothetically,” Flynn could have been charged with treason and told the former lieutenant general that, “arguably, you sold out your country.”

Sullivan later walked back those comments.

Still, Sullivan spoke at length Tuesday about the seriousness of Flynn's crime, at one point expressing “disdain” for his actions. He cautioned Flynn that, if they proceeded to sentencing on Tuesday, he could not rule out prison.

“I'm going to be frank with you: This crime is very serious,” Sullivan said, highlighting more than once how Flynn was a high-ranking official who lied to the FBI on White House grounds.

Sullivan described how Flynn worked as an unregistered agent of a foreign power while serving as a Trump adviser, later correcting his statement. But in that exchange, the judge pointed to a flag behind him and said Flynn's conduct arguably undermined “everything this flag” stands for.

At the start of Tuesday's hearing, the judge pressed defense attorneys about a court memo that appeared to suggest federal investigators led Flynn to lie during his January 2017 FBI interview. The filing noted Flynn was not warned that lying to the FBI was illegal, and that he did not have counsel present during the interview.

Sullivan said the filing “raised some concerns” with the court, and questioned how it was consistent with Flynn's acceptance of responsibility.

Kelner explained the filing was meant to distinguish Flynn's case from those of former Trump campaign adviser George Papadopoulos and former Skadden associate Alex van der Zwaan, who were sentenced to prison terms of 14 days and 30 days, respectively. The “aggravating circumstances” in the Papadopoulos and van der Zwaan cases don't apply to Flynn, Kelner said, adding the former national security adviser “fully accepts responsibility” and “stands by his guilty plea.”

Kelner later emphasized that Flynn's attorneys, not Flynn, had written that filing.

The judge also squarely asked Flynn in the morning if he wished to challenge the circumstances in which the FBI interviewed him.

“No, your honor,” Flynn replied.

Asked if he was continuing to accept responsibility for his false statements, Flynn said: “I am, your honor,” before he re-entered his guilty plea before the court.

Flynn pleaded guilty last December to lying to federal investigators, and misleading investigators about his contact with ex-Russian Ambassador Sergey Kislyak during the presidential transition. He also admitted to filing false paperwork with DOJ related to his lobbying work for Turkey.

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