Judge delays sentencing Flynn after rebuke: 'Arguably, you sold your country out!' Flynn is facing up to six months in prison for lying to the FBI.

Michael Flynn's defense attorney asked a federal judge to delay sentencing after the judge unleashed a blistering attack on the former Trump adviser's conduct.

Judge Emmet Sullivan, a veteran of the bench who received his judicial appointments from Presidents Ronald Reagan, George H.W. Bush and Bill Clinton, admonished Flynn at a hearing on Tuesday in Washington, D.C., for lying to the FBI, which he said was made worse because of where it occurred.

"In the White House! In the West Wing. By a high ranking security officer who up to that point had an unblemished career of service to his country,” the judge said. “It's a very serious offense. ... Arguably, this undermines everything this flag over here stands for! Arguably, you sold your country out!"

The judge agreed to the postponement and set the next status report for March.

The judge’s comments appeared to be a reversal of fortune for the man who spent months campaigning for Trump and served briefly as Trump’s national security adviser.

Prosecutors had asked for leniency – no jail time – in sentencing Flynn because he had cooperated extensively with the Special Counsel Robert Mueller's ongoing investigation of Russian interference in the 2016 election.

"We believe that he has accepted responsibility -- not just his statements to the court today but throughout the proceedings," said Brandon L. Van Grack, a prosecutor from Mueller's office.

Flanked by his wife, and supported by his son and several of his eight siblings, Flynn responded methodically to the judge’s questions, declining to reverse his guilty plea or argue that he lied as a result of coercion by the FBI.

But the judge’s comments substantially changed the mood in the courtroom -- especially when he began to question prosecutors about whether they ever considered a charge of treason -- which appeared to stem from his concern about Flynn's work on behalf of the Turkish government until just days before Trump identified him as the man who would serve as his first national security adviser.

“Is there an opinion about the conduct of the defendant that rises to treasonous on the defendants part?” the judge asked Van Grack, who said the special counsel had not considered leveling that charge. “Hypothetically could he have been charged with treason?” the judge asked again.

Van Grack replied that it was “such a serious question I'm hesitant to answer it.”

After a brief recess, the judge walked-back the incendiary question, saying "I wasn't suggesting he committed treason!"

"There are a lot of conspiracy theorists out there. I am not taking the elements of any of the uncharged offenses under consideration at the time of sentencing,” he said.

Flynn had done lobbying work between August and November 2016 for Turkey that, according to Justice Department filings, “could be construed to have principally benefited the Republic of Turkey.” Flynn’s company, the Flynn Intel Group, was paid at least $530,000 for the work, and the contract ended on November 15, just three days before Trump named Flynn as the man he wanted to take on the top White House post.

It has been more than a year after he pleaded guilty to lying to the FBI about his contacts with the Russian ambassador to the United States and agreed to cooperate with Mueller's probe.

He faces up to six months in prison, but in a sentencing memo filed last week, Mueller told the judge that Flynn had provided investigators with "substantial assistance" in more than a dozen interviews, and that because he flipped early, "a sentence at the low end of the guideline range -- including a sentence that does not impose a term of incarceration -- is appropriate and warranted."

But last-minute intrigue was thrown into what was anticipated to be a cut-and-dry sentencing process Monday evening when the government filed the FBI's formerly secret internal report based on two investigators' interview with Flynn on Jan. 24, 2017.

The February 2017 document, called a "302" in FBI parlance, shows how the agents went into the meeting armed with knowledge of conversations Flynn had during the transition period after the election with Russian Ambassador Sergey Kislyak, including calls and text messages they exchanged in the U.S. and while Flynn and his wife were on vacation in the Dominican Republic.

The report shows Flynn repeatedly said "no" or didn't remember when they asked him specific questions about his contacts with Kislyak on the subject of a UN vote on Israeli settlements the Obama administration abstained from and sanctions the Obama White House imposed on Russia for interfering with the 2016 presidential election.

The reason the judge ordered the 302 placed on the public docket was that Flynn's legal team raised the question in their sentencing memo to the judge of whether FBI agents tried to lay a perjury trap on Flynn. The government, in response, said, "When the defendant said he did not remember something they knew he said, they used the exact words the defendant had used in order to prompt a truthful response."

Judge Sullivan said the report is "relevant to Mr. Flynn's sentencing," though he did not indicate how it will factor into his ruling on Flynn's sentence.

Flynn's plea precipitated a remarkable fall for the decorated military veteran. A career military intelligence officer who served in the 82nd Airborne Division, he became an intelligence innovator after 9/11 by attacking complex terrorist networks in war zones. He was tapped to lead the Defense Intelligence Agency in 2012 but was pushed out by the Obama White House in 2014. In retirement, he set up a consulting firm called the Flynn Intel Group outside Washington.

Flynn was an early Trump supporter and became outspoken on the campaign trail. He led national security during the transition -- a period during which he spoke to Russia's ambassador before President Trump was sworn in -- and he briefly served as his national security adviser. He was fired by Trump after just 21 days in the position for lying to Vice President Mike Pence about whether he had discussed lifting sanctions against Russia with its ambassador during the transition.

When Flynn pleaded guilty a year ago, the President tweeted that Flynn had "lied to the Vice President and the FBI" but last week claimed in another tweet that Flynn got "a great deal" from Mueller.

On Tuesday morning, President Donald Trump wished his former national security adviser "good luck" in a tweet.

Last week, Flynn's attorney Robert Kelner filed a lengthy sentencing memo which laid out his military accomplishments and awards, and also strongly suggested the FBI had been disingenuous in its treatment of Flynn, perhaps an attempt to restore some luster to the reputation of a man who had earned three sparkling stars on his uniform.

In the defense sentencing memo, Flynn's family, friends and former colleagues cast him as selfless in serving his country and saving lives, from his boyhood rescue of two toddlers in the path of a runaway car in Rhode Island to handing his own armored vest to another officer during a suicide vehicle bomb attack in Afghanistan.

Letters described how his efforts to help destroy al-Qaeda in Iraq -- which eventually became ISIS -- saved thousands of lives and revealed how Flynn personally directed the entire NATO-led force in a failed effort to prevent Army Pvt. Bowe Bergdahl's captors "from trafficking him across the Pakistan border."

"For those who bore witness to these actions, Flynn was the embodiment of selfless service and military values," wrote retired Army Col. Yvette Hopkins in the letter included in Flynn's sentencing memo.

Flynn later told British documentary filmmaker Sean Langan that Bergdahl, who was court-martialed and pleaded guilty to charges of desertion and misbehavior before the enemy last year, was worthy of mercy.

"So the guy deserted his men, his soldiers, his squad -- no doubt," Flynn said in 2016. "[But] I don't think he should serve another day in any sort of confinement or jail or anything like that, because frankly, even though he put himself into this situation to a degree, we -- the United States government and the United States military — put him in Afghanistan."

Retired Army Brig. Gen. Donald Bolduc, who commanded special operations in Afghanistan and Africa, told ABC News that Flynn is also worthy of such mercy, having endured the crucible of a long investigation that "has had negative consequences on an inherently good man and family."

"Despite the political issues and the legal issues he is experiencing, Lt. Gen. Flynn in my assessment is a good man," Bolduc said. "He knows more than anyone about personal accountability. I am sure no one understands more the consequences of being untruthful during an investigation than Lt. Gen. Flynn. As we all do, I am sure he has reflected on any mistakes he made and is moving forward to make amends and learn."

Those closest to Flynn told ABC News that he is eager to be rid of that spotlight from political critics, news media and criminal investigators.

In the last year, he has not granted any interviews, instead seeking the privacy of the the Rhode Island community he grew up in, passing his days surfing and spending time with his large family.

He has not been entirely absent from the political scene, however. He spoke at one fringe Republican's early campaign event earlier this year and made a rare speech to accept an award at a conservative political conference in September.

ABC News' Allison Pecorin contributed to this report.