(CNN) -- Former Trump national security adviser Michael Flynn pleaded guilty Friday to lying to the FBI about conversations with Russia's ambassador and disclosed that he is cooperating with the special counsel's office.
Flynn is the first person inside the Trump administration to be reached by special counsel Robert Mueller's probe, and the developments are a sign that the investigation is intensifying.
In court Friday morning, Flynn's only comments were to answer yes and no to questions from the judge. He told the judge he has not been coerced to plead guilty or been promised a specific sentence.
In a statement, Flynn said he acknowledged that his actions "were wrong, and, through my faith in God, I am working to set things right.
"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 of our country. I accept full responsibility for my actions," he said.
Flynn is the fourth connected to his campaign to be charged as part of Mueller's investigation into possible collusion between the Russian government and members of President Donald Trump's team, as well as potential obstruction of justice and financial crimes.
Trump's former campaign chairman Paul Manafort and his deputy Rick Gates were indicted last month; they pleaded not guilty. And Trump campaign foreign policy adviser George Papadopoulos pleaded guilty for making a false statement to the FBI over contacts with officials connected to the Russian government.
'This is a win for the White House'
The White House said late Friday morning that "nothing about the guilty plea or the charge implicates anyone other than Mr. Flynn.
"The conclusion of this phase of the special counsel's work demonstrates again that the special counsel is moving with all deliberate speed and clears the way for a prompt and reasonable conclusion," Ty Cobb, a White House lawyer, said in a statement.
White House allies initially tried to put a positive spin on the news.
One person familiar with the mood in the West Wing insisted top White House officials were breathing a sigh of relief.
"People in the building are very happy," the source said. "This doesn't lead back to Trump in any way, shape or form." The source noted that Flynn is being charged for making false statements, but not for any improper actions during the campaign.
"This is a further indication that there's nothing there," the source said. "This is a win for the White House."
A source with knowledge of the legal team's thinking tells CNN the Flynn plea "is not going to be a problem" for the President, though it could be a problem for people who worked with Flynn. The source said legal exposure for others would depend on what they might have said to the special counsel.
A source who advises the administration on strategy said this was expected.
"Poor judgment. But this was expected. Trump fired him for lying to (Vice President Mike Pence). Of course, he lied to the FBI, too," the source said.
And another source, who is close to Trump, attempted to downplay the severity of the charge against Flynn by noting that lying in Washington is not new. The source maintained that he was still not worried about any potential cooperation between Flynn and the prosecutors.
Hillary Clinton, whom Trump defeated in the 2016 general election and was the focus of the "lock her up" chant first popularized by Flynn at the Republican National Convention, declined through a spokesman to comment on Friday's developments.
Stunning downfall for Flynn
Flynn's lawyers have previously criticized media reports about his connection to the Russia investigation as peddling "unfounded allegations, outrageous claims of treason, and vicious innuendo directed against him." Flynn hasn't spoken publicly since his ouster in February.
The charges mark yet another stunning downfall for Flynn, 58, a retired general who rose to the highest ranks of the Army over a three-decade career -- only to see him drummed out of the military by the Obama administration before unexpectedly rising again on the heels of Trump's election victory.
A key campaign surrogate and adviser during Trump's presidential campaign, Flynn was tapped as Trump's national security adviser in November 2016, a senior White House job that put him in a vital role for all of the administration's national security and foreign policy decisions.
Though he wasn't initially considered for the top job, Trump's daughter, Ivanka Trump, and son-in-law Jared Kushner made it clear to the Trump transition team that they wanted him there, CNN has reported.
Flynn would hold the job less than a month, resigning from the post after he misled Pence and then-chief of staff Reince Priebus about his conversations with then-Russian Ambassador to the US Sergey Kislyak in which they discussed US sanctions against Russia.
Flynn is also the spark of potential trouble for the President in Mueller's probe, as the special counsel is investigating potential obstruction of justice in the firing of FBI Director James Comey.
Comey testified before the Senate intelligence committee that Trump asked him to drop the Flynn probe during a February Oval Office meeting not long after Flynn resigned as national security adviser.
Talking about sanctions
Flynn's conversations with Kislyak attracted scrutiny from federal investigators as part of the FBI's broader counterintelligence investigation of Russian activities in the US, and the calls were captured by routine US eavesdropping targeting the Russian diplomat, CNN has reported.
The Trump transition team acknowledged that Flynn and Kislyak spoke on the day in December 2016 that the Obama administration issued new sanctions against Russia and expelled 35 diplomats, but they insisted the conversation did not include sanctions — including denials that Pence and Priebus later repeated on national television.
Flynn resigned on February 13 after reports that he and Kislyak had spoken about sanctions and that the Justice Department had warned the White House that Flynn was potentially vulnerable to blackmail by the Russians.
Details of how the DOJ warned the White House about Flynn's conduct were revealed months later in stunning testimony from former acting Attorney General Sally Yates, who said that she "believed that General Flynn was compromised with respect to the Russians" because of the misleading denials.
The charging document states that Flynn made a false statement to the FBI when he stated that in December 2016 he did not ask Kislyak "to refrain from escalating the situation in response to sanctions that the United States had imposed against Russia that same day; and Flynn did not recall the Russian ambassador subsequently telling him that Russia had chosen to moderate its response to those sanctions as a result of his request."
The document also says that Flynn falsely said he did not ask Kislyak to delay the vote on a pending United Nations Security Council resolution.
After his resignation, Flynn and his businesses quickly became a major interest of the House and Senate intelligence committee Russia probes.
But in March, Flynn's lawyer dropped a bombshell: "General Flynn certainly has a story to tell, and he very much wants to tell it, should the circumstances permit," attorney Robert Kelner said, adding that Flynn was seeking immunity in exchange for his testimony. Committee leaders quickly rejected the offer.
Flynn has not spoken to the congressional committees and has refused requests to appear voluntarily.
Warnings before Trump took office
Flynn's legal issues stem from foreign payments he received after he started his own consulting firm.
Flynn founded the Flynn Intel Group after he retired from the military in 2014. The Obama White House pushed him out of his role as head of the Defense Intelligence Agency (DIA), the military's intelligence arm. Flynn was fired over claims he was a poor manager, though he says he was ousted by Obama administration officials unwilling to listen to his warnings about the rise of ISIS and an increasingly aggressive Iran.
Before he was named national security adviser, the FBI began investigating Flynn for secretly working during the presidential campaign as an unregistered lobbyist for Turkey, an investigation he disclosed to the Trump transition team before Trump took office.
Flynn wasn't the only Trump associate who faced scrutiny over foreign lobbying laws -- Manafort also filed a retroactive registration earlier this year for work he previously did in Ukraine.
Federal investigators were probing whether Flynn was secretly paid by the Turkish government as part of its public campaign against Fethullah Gulen, a critic of Turkish President Recep Tayyip Erdogan who lives in exile in Pennsylvania. Erdogan blames Gulen and his supporters for plotting the failed Turkish coup last summer.
As part of his pro-Turkey lobbying, Flynn and his colleague held meetings during the Trump transition with Turkish representatives. According to The Wall Street Journal, Flynn and his son were offered as much as $15 million to forcibly remove from the United States a Turkish cleric wanted by Turkey.
CNN's legal analysts say the alleged plan to kidnap Gulen and subvert the US legal process would directly violate the US criminal code and could carry a punishment of as much as 20 years in federal prison. Lawyers for Flynn said the allegations "ranging from kidnapping to bribery" are completely false.
Flynn's lobbying firm was paid $530,000 by Inovo BV, a company owned by Turkish businessman Ekim Alptekin, during the final months of the US presidential campaign. The Flynn Intel Group, which is no longer active, was tasked with producing an anti-Gulen documentary, though the final product never surfaced. Flynn also penned an op-ed criticizing Gulen, which was published on Election Day.
In March, Flynn's firm retroactively registered as a foreign agent that lobbied for the Turkish government.
Payments from Russian businesses
Flynn has also been scrutinized for his work with Russian businesses.
In his initial financial disclosure form filed in February with the Office of Government Ethics, Flynn left off payments of thousands of dollars from RT, the Russian government-funded television network and two other Russian companies. Flynn subsequently added the payments in an amended disclosure.
Among the payouts, Flynn received $33,000 of a $45,000 speaking fee for a 2015 speech at a Moscow event hosted by RT, where he sat at the same table as Russian President Vladimir Putin.
Flynn's presence at the gala celebrating RT's 10th anniversary raised eyebrows among his critics. The US intelligence community said earlier this year that the Kremlin uses RT to push propaganda on American audiences, and that the English-language channel was involved in the effort to interfere in the election.
In 2015, the former DIA chief received $11,000 each from a subsidiary of Kaspersky Lab — the Russian cybersecurity firm banned from US government use in September — and a Russian cargo airline company.
Democrats on the House oversight committee accused Flynn of lying about the RT payments in his 2016 security clearance renewal, saying in a May letter that Flynn told investigators the payments were from "US companies." They released documents earlier this year that showed that the money originally came from RT and was funneled through his US-based speakers bureau, which took a commission.
In 2014, Flynn was warned by the DIA against taking payments from foreign governments, according to documents released earlier this year by the oversight committee.
Trump said in May that he hadn't known that Flynn took payments from Russia and Turkey.
Flynn's son also faces scrutiny
Flynn's son, Michael Flynn Jr., has also faced scrutiny from Mueller's investigation, though he was not charged on Friday.
Flynn Jr. served as his father's chief of staff and top aide at their consulting firm, the Flynn Intel Group. In that capacity, Flynn Jr. joined his father on overseas trips, such as Moscow in December 2015 when Flynn dined with Putin at the RT gala.
The younger Flynn has a penchant for spreading conspiracy theories on Twitter. He has smeared Trump's opponents -- ranging from Clinton to Republican Sen. Marco Rubio -- as well as Muslims and other minorities. Most prominently, he peddled the debunked claim that a Washington pizzeria was a front for Democrats to sexually abuse children.
These posts caught up to Flynn Jr. when he was dropped from the Trump transition. As the "Pizzagate" conspiracy spread, Pence, who ran the transition, insisted that Flynn Jr. have "no involvement in the transition whatsoever." But CNN reported that Flynn Jr. had a transition email address and that the transition asked for him to receive a security clearance. Pence later acknowledged that Flynn Jr. had helped his father prepare for the national security adviser position.
Flynn Jr. has remained defiant as the investigation has heated up. Days after Manafort and Gates were indicted, Flynn Jr. sent a message to his critics: "The disappointment on your faces when I don't go to jail will be worth all your harassment."