(CNN) -- The sentencing for President Donald Trump's former national security adviser Michael Flynn was postponed until 2019 after a dramatic federal court hearing Tuesday.
Flynn, who pleaded guilty last year, said "I was aware" that lying to the FBI was a crime, but prosecutors from special counsel Robert Mueller's office had called for him to get little to no jail time because he has cooperated extensively. They also said Flynn may continue to cooperate in a future trial.
Judge Emmet Sullivan of the US District Court for the District of Columbia said he was "not hiding my disgust, my disdain for your criminal offense."
"I want to be frank with you, this crime is very serious," Sullivan said. "Not only did you lie to the FBI, you lied to senior officials in the incoming administration."
"All along, you were an unregistered agent of a foreign country while serving as the national security adviser to the President of the United States," Sullivan said. "That undermines everything this flag over here stands for. Arguably you sold your country out."
Sullivan later corrected himself, noting Flynn's foreign lobbying ended prior to the beginning of the Trump administration.
Both sides now have until March 13 to file a status report with the court.
Flynn left the courthouse without speaking to reporters.
Flynn has given Mueller a key witness on some of the most scrutinized moments during the Trump campaign, transition and first month in the White House -- while also turning the former Army lieutenant general into a political cause backed by conservatives wary of Mueller's approach.
Trump himself wished Flynn "good luck" in a Tuesday morning tweet, adding that it "will be interesting to see what he has to say."
Despite Flynn's admissions that he lied about three things -- including policy requests he made to then-Russian Ambassador Sergey Kislyak during the transition -- Mueller's team has asked the judge to sentence Flynn to minimal or even no time.
Three previous defendants in Mueller's probe -- Trump's former personal attorney Michael Cohen, the Dutch lawyer Alex van der Zwaan and former Trump campaign adviser George Papadopoulos -- pleaded guilty to the same crime of lying. Each received sentences that included prison time. But none of those men helped investigators as broadly, willingly or sincerely as Flynn, Mueller's team has said.
Another defendant, former Trump campaign deputy Rick Gates, also pleaded guilty to a lying charge in Mueller's probe. He continues to cooperate with the investigation and has no set sentencing date.
Flynn's sentencing has been shaded over the past three weeks by criticism of the FBI's actions when it first approached him in the White House on January 24, 2017.
Flynn's defense team first raised the issue in a memo to Sullivan last week. The defense lawyers argued that Flynn should be spared jail time because he had lied under different circumstances than van der Zwaan and Papadopoulos, who had been warned they could be prosecuted for lying to the FBI.
Flynn spoke to the FBI agents with no lawyer present and hadn't been warned of the potential legal consequences. He also did not involve the White House counsel's office, and the FBI did not involve the Justice Department in his interview.
Flynn was so relaxed, investigators said, that they did not have the impression that he was lying during the interview, according to memos from the agents. Even so, the FBI knew that when Flynn said he hadn't asked for certain responses from Kislyak to the American sanctions against Russia or a United Nations Security Council resolution, he was lying.
Tuesday, Sullivan asked Flynn's attorney Stephen Anthony if the former national security adviser was "entrapped by the FBI." Anthony said, "No, your Honor."
Another FBI memo about the January 24, 2017, interview, released Monday night, further solidified that Flynn wrongly denied he had tried to influence the Russian government's reaction to sanctions and intentions at the UN.
Flynn first met Kislyak in 2013 while director of the Defense Intelligence Agency, and he had developed the relationship with the Russian government since then. Court documents made public last year show that members of Trump's transition team knew about Flynn's requests to the ambassador a month before the inauguration.
Flynn is also central to the potential obstruction of justice case surrounding Trump's interactions with former FBI Director James Comey. According to a memo Comey wrote in February 2017, the President asked him to drop the investigation into Flynn.
Mueller's team has described on multiple occasions how Flynn misled members of the Trump administration about his contacts with Kislyak, which then prompted those public officials to share false information with the American public.
'Could he have been charged with treason?'
Sullivan stunned the courtroom when he asked if Flynn conduct "rises to the level of treasonous activity."
Prosecutor Brandon Van Grack, speaking for the special counsel's office, said prosecutors did not consider charging Flynn with treason.
Then Sullivan asked again: "Could he have been charged with treason?"
Later, Sullivan walked back his treason questions. "I'm not suggesting" Flynn committed treason, he said.
"I was just trying to determine the benefit and the generosity of the government," he said. "Don't read too much into the questions I ask."
Sullivan's closing words to the courtroom were: "Happy holidays."
Aside from Flynn's conversations with the Russian, he admitted to lying about his lobbying work for the Turkish government as it sought to build American support for the extradition of a cleric and political opponent living in Pennsylvania.
Flynn's two former business associates were indicted by the Justice Department on Monday for working on this project, which included Flynn authoring an op-ed in a Washington newspaper that sympathized with the current Turkish government and demonized the cleric. The op-ed published on Election Day 2016. The former business associates also accepted payments for the work through Flynn's company, the Flynn Intel Group, according to the charging document.
One of the men, Flynn Intel Group co-founder Bijan Rafiekian, also known as Bijan Kian, appeared in a Virginia courtroom Tuesday and plead not guilty to charges of conspiracy and illegally acting as a foreign agent in the US.
The other defendant in the case, a Dutch-Turkish businessman, is charged with the same two crimes plus lying to the FBI. The businessman, Kamil Ekim Alptekin, lives in Istanbul and has not appeared in US court.