President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE’s former national security adviser Michael Flynn has pleaded guilty to lying to federal investigators about his contacts with Russia’s ambassador to the United States.

Flynn, a former Obama-era defense official turned surrogate for Trump’s campaign, is now cooperating with special counsel Robert Mueller’s investigation into whether there was collusion between the Trump campaign and Moscow.

His plea deal came about a month after Mueller unveiled charges against former Trump campaign officials Paul Manafort and Richard Gates and revealed that George Papadopoulos, a low-level campaign adviser, had pleaded guilty to lying to FBI agents.

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Here are the five major takeaways from Flynn’s guilty plea.

The Russia probe is getting closer to the White House

Flynn is the first member of the Trump administration to be implicated in the special counsel’s investigation.

He served as national security adviser for 24 days before he was forced to resign after reports surfaced that he had discussed sanctions with then-Russian Ambassador Sergey Kislyak during the transition period, despite telling Vice President Pence he had not.

Flynn played a prominent role in Trump’s campaign as a foreign policy adviser and surrogate, delivering a memorable speech at the Republican National Convention during which he led a “lock her up” chant about Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE.

According to court filings, Flynn, while he was national security adviser, lied to FBI agents when he told them that he did not tell Kislyak in December 2016 to “refrain from escalating the situation” in response to sanctions that the Obama administration had levied on Moscow the same day. He also lied when he said he did not ask Kislyak to delay or defeat a vote on a pending United Nations Security Council resolution, the documents say.

The developments make it difficult for the White House to claim that Mueller’s findings are unrelated to the campaign or the administration.

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“It is a nightmare for Donald Trump,” Judge Andrew Napolitano said on Fox News.

Still, legal experts caution that it is too soon to assess the value of Flynn to Mueller’s investigation — or what he might have on the White House.

“People are getting ahead of their skies in assuming that this plea agreement represents an existential threat to the Trump administration,” said Jonathan Turley, a legal professor at George Washington University.

But, Turley, a contributor for The Hill, added, “it could represent a threat to other individuals like Jared Kushner,” Trump’s son-in-law and senior adviser who is said to have met with Kislyak and Flynn in December.

Senior Trump transition officials directed Flynn’s Russia contacts

According to court documents, Flynn and a senior member of Trump’s transition team discussed whether he should broach the topic of sanctions with Kislyak during the Dec. 29 conversation.

Flynn is said to have contacted the official, who was with other transition members at Trump’s Mar-a-Lago resort in Palm Beach, Fla., on Dec. 29 to discuss what to communicate to Kislyak about U.S. sanctions on Moscow.

The two discussed sanctions, “including the potential impact of those sanctions on the incoming administration’s foreign policy goals,” and agreed that the transition team “did not want Russia to escalate the situation,” according to the documents.

A Dec. 29 pool report indicates that current administration officials Stephen Miller, Kellyanne Conway, and K.T. McFarland, as well as former White House aides Stephen Bannon and Reince Priebus, were all with Trump at Mar-a-Lago on the day Flynn made the call.

The filings show that multiple members of Trump’s transition team knew that Flynn discussed sanctions with Kislyak after the phone conversation occurred.

Prosecutors also say that a senior member of the transition team on Dec. 22 directed Flynn to contact officials from Russia and other governments about their stance on the U.N. resolution “and to influence those governments to delay the vote or defeat the resolution.”

Multiple reports have identified Kushner as that official. The special counsel's office declined to comment.

The revelations have opened up speculation about the identity of the officials who knew about and directed Flynn’s Russia contacts.

Flynn seems to be getting a good deal

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Speculation has swirled for months that Flynn would be charged in Mueller’s probe.

He has faced scrutiny stemming from his failure to disclose income from Russia- and Turkey-linked entities, which are potential violations of the Foreign Agents Registration Act.

Flynn’s consulting firm was paid $530,000 during the campaign for work that may have helped benefit the Turkish government.

He was also reportedly under investigation for a scheme that would have led to the forced extradition of a Muslim cleric considered an enemy of the Turkish government in exchange for millions of dollars, according to multiple outlets.

On Friday, Flynn pleaded guilty to one count of making false statements to the FBI, which carries a maximum five years in prison. According to the plea deal Mueller negotiated with Flynn, he will face at most six months in prison and a $9,500 fine.

Stephen Vladeck, a University of Texas law professor, described the charges against Flynn as a “sweetheart deal.”

“I think there were so many other potential charges to level against Flynn,” Vladeck said.

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In addition to protecting himself from further charges, Flynn is said to be cooperating with the investigation to guard his son from potential criminal prosecution.

“My guilty plea and agreement to cooperate with the Special Counsel’s Office reflect a decision I made in the best interests of my family and our country,” Flynn said in a statement.

He could have extremely valuable information

The favorability of Flynn’s plea deal has led some to speculate on the potential value of the information he has, through his lawyers, offered to Mueller.

“This is a good enough deal that one has to wonder what Flynn brought to the table,” Turley said. “That’s what would worry me if I were on the Trump legal team, is that this deal is a bit too good as a mere prosecutorial housekeeping move.”

Flynn’s proximity to Trump during the campaign and transition, as well as into the early days of the administration, has raised questions about what he might know about the president and his inner circle.

ABC News has corrected a report that Flynn is prepared to testify that Trump directed him to make contact with Russians during the campaign.

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“The question that everyone should ask themselves is not what Flynn has but against whom,” Vladeck observed. “With an indictment already pending against Manafort, who else would it be worth it to Mueller to plead out Flynn in exchange for dirt on?”

“We don’t know what Flynn knows, but if you just think logically from Mueller’s perspective who would be higher on the food chain, the list after Flynn is a lot shorter than the list after Manafort,” he continued.

No signs of end to Mueller’s investigation

Mueller has a broad mandate to investigate any potential criminal activity arising from his investigation into potential coordination between the Trump campaign and Moscow.

Friday’s developments signal that his investigation is moving forward methodically, and that it could be a long way from reaching its conclusion.

Mueller’s team has reportedly begun interviewing high-level current and former White House officials, including Priebus and communications director Hope Hicks.

Ron Hosko, a former FBI official who served under Mueller, speculated that Friday’s developments signal Mueller has more work to do.

“I think Mueller is harvesting today — and I’m not disparaging what they’re doing — I think they’re harvesting the low-hanging fruit,” Hosko said. “That’s the starting point for an investigation.”

— This report was updated at 7:30 a.m.