Washington(CNN) Embattled White House national security adviser Michael Flynn resigned Monday night, an abrupt end to a brief tenure.
His departure came just after reports surfaced that the Justice Department warned the Trump administration last month that Flynn misled administration officials regarding his communications with the Russian ambassador to the United States and was potentially vulnerable to blackmail by the Russians.
"I inadvertently briefed the Vice President-elect and others with incomplete information regarding my phone calls with the Russian ambassador. I have sincerely apologized to the President and the Vice President, and they have accepted my apology," Flynn wrote, according to a copy of his resignation letter obtained by CNN.
"I am tendering my resignation, honored to have served our nation and the American people in such a distinguished way," he wrote. "I know with the strong leadership of President Donald J. Trump and Vice President Mike Pence and the superb team they are assembling, this team will go down in history as one of the greatest presidencies in US history."
The move comes less than a month into the job, making him one of the shortest-serving senior presidential advisers in modern history.
Gen. Keith Kellogg will be the interim national security adviser, multiple sources tell CNN. He most recently served as National Security Council chief of staff.
A senior administration official said Kellogg, retired Gen. David Petraeus and former Vice Admiral Bob Harward are possible replacements for Flynn. Another senior official told CNN Tuesday that Harward is considered the top contender for the job.
Petraeus is going to the White House Tuesday, according to sources inside and close to the administration.
"He is making a run" for the job, one source said, but noted "he has a lot of baggage."
The sudden exit marks the most public display yet of disarray at the highest levels of the new administration, which has faced repeated questions over a slew of controversies and reports of infighting among senior aides during its first three weeks.
The resolution had been heading this way for three days, an administration source told CNN.
More than whether he really had a conversation with the Russians about sanctions, the key issue internally was whether he told the truth to Pence, the source said.
How to get fired by the president of the United States
The White House concluded at the very least, Flynn didn't mean to mislead the vice president, but may have because he couldn't remember what he said to the Russians.
"Not remembering is not a quality we can have for the national security adviser," the source said.
An administration source said that Trump "hung in there" when it came to Flynn, but there was a "flood of information" that finally made it clear he had to resign.
Asked if Trump is disappointed, another administration official said: "He's moving on."
'Full classified briefing'
A pair of Democratic lawmakers -- Reps. John Conyers, Jr., top Democrat on the House Judiciary Committee, and Elijah Cummings, top Democrat on the House oversight Committee -- sent a request for a "full classified briefing" on the circumstances surrounding Flynn to the Justice Department and FBI Monday night following Flynn's resignation.
"We in Congress need to know who authorized his actions, permitted them and continued to let him have access to our most sensitive national security information despite knowing these risks. We need to know who else within the White House is a current and ongoing risk to our national security," they wrote in a statement.
They added: "This new disclosure warrants a full classified briefing by all relevant agencies, including the Department of Justice and the FBI, as soon as possible and certainly before Thursday, February 16. We are communicating this request to the Department of Justice and FBI this evening."
The shakeup now leaves Trump without one of his closest and longest-serving advisers. Flynn had counseled Trump on foreign policy and national security matters since early in the 2016 presidential race.
Flynn was not able to definitively refute a Washington Post story late last week that his conversations with Russian Ambassador Sergey Kislyak included communication about the sanctions. It is illegal for unauthorized private citizens to negotiate with foreign governments on behalf of the US.
The controversy intensified after the report put Vice President Mike Pence and several senior White House advisers in an uncomfortable position, as they had denied in TV interviews weeks earlier that Flynn discussed sanctions with the ambassador. Some administration officials said Flynn must have misled Pence and others.
"The knives are out," a White House official told CNN on Friday, noting that "there's a lot of unhappiness about this."
Many expressed concern at the idea that Flynn, a retired lieutenant general who headed the Defense Intelligence Agency, would discuss sanctions with a foreign official whose calls are regularly monitored by US intelligence and law enforcement agencies.
A US official confirmed to CNN on Friday that Flynn and Kislyak did speak about sanctions, among other matters, during a December call.
But after the call was made public, Pence told CBS News on January 15 that Flynn did not talk with Kislyak about the sanctions, which the Obama administration recently levied due to Russia's alleged interference in the 2016 elections.
Trump's nominees and their confirmation hearings
Vice President Mike Pence, right, administers the oath of office to Dan Coats, the new director of national intelligence, on Thursday, March 16. Coats was accompanied by his wife, Marsha. He was confirmed by the Senate the day before.
Coats speaks on Capitol Hill before his confirmation hearing in February. The former US senator from Indiana
was the US ambassador to Germany in the first term of George W. Bush's administration.
New Energy Secretary Rick Perry speaks at his swearing-in ceremony in Washington on Thursday, March 2. The former Texas governor was confirmed
by a Senate vote of 62-37.
Perry is sworn in before his confirmation hearing in January. During his testimony,
Perry cast himself as an advocate for a range of energy sources, noting that he presided over the nation's leading energy-producing state. He also said he regrets once calling for the Energy Department's elimination.
Ben Carson is joined by his wife, Candy, and his granddaughter Tesora as he is sworn in as the secretary of housing and urban development on March 2. The renowned neurosurgeon and former presidential candidate was confirmed
by a vote of 58-41.
Carson greets Tesora prior to testifying before the Senate Committee of Banking, Housing and Urban Affairs in January. In his opening statement,
he noted that he was raised by a single mother who had a "third-grade education" and made the case that he understands the issues facing the millions of people who rely on HUD programs.
New Interior Secretary Ryan Zinke signs an official document after he was confirmed by the Senate
on Wednesday, March 1. The former congressman from Montana was joined by his wife, Lolita, as well as Vice President Mike Pence, US Sen. Steve Daines and Montana Attorney General Tim Fox.
Zinke, a former Navy SEAL, is sworn in before his confirmation hearing
in January. He pledged to review Obama administration actions that limit oil and gas drilling in Alaska, and he said he does not believe climate change is a hoax.
Pence swears in new Commerce Secretary Wilbur Ross as Ross' wife, Hilary, stands by on Tuesday, February 28. The billionaire was confirmed by the Senate
by a vote of 72-27.
Ross, center, waits to be introduced by US Sen. Marco Rubio, right, at his confirmation hearing in January. At the hearing, Ross said he wants countries that resort to "malicious" trading tactics to be "severely" punished. He pointed the finger at China,
which he called "the most protectionist country of very large countries."
Supreme Court justice Samuel Alito swears in Scott Pruitt as the new administrator of the Environmental Protection Agency on Friday, February 17. Holding the Bible is Pruitt's wife, Marlyn, and they were joined by their son, Cade. Pruitt, the former attorney general of Oklahoma, was confirmed by the Senate 52-46.
Pruitt testifies at his confirmation hearing
in January. Pruitt said he doesn't believe climate change is a hoax, but he didn't indicate he would take swift action to address environmental issues that may contribute to climate change. He said there is still debate over how to respond.
Pence shakes hands with Mick Mulvaney after swearing him in as the new director of the Office of Management and Budget on Thursday, February 16. Mulvaney's wife, Pam, looks on. Mulvaney had been a congressman since 2011.
Mulvaney testifies before the Senate Budget Committee in January. He didn't back off his views
that entitlement programs need revamping to survive -- and he didn't back away from some of his past statements on the matter. President Donald Trump, during his campaign, pledged not to touch Social Security or Medicare.
McMahon speaks during her confirmation hearing. She stepped down from her WWE duties in 2009 and ran for the Senate in 2010 and 2012.
Pence watches David Shulkin, the new secretary of the Veterans Affairs Department, speak at his swearing-in ceremony on February 14. Shulkin was confirmed by a unanimous vote
in the Senate.
Shulkin speaks at his confirmation hearing. He was the VA's undersecretary for health,
a position in which he oversaw more than 1,700 health care sites across the United States.
Mnuchin arrives for his confirmation hearing in January. Mnuchin, a former Goldman Sachs banker, faced policy questions
about taxes, the debt ceiling and banking regulation.
Pence shakes hands with Health and Human Services Secretary Tom Price -- who was accompanied by his wife, Betty -- after a swearing-in ceremony on Friday, February 10. Price, a former congressman from Georgia, was confirmed 52-47
in a middle-of-the-night vote along party lines.
Price testifies at his confirmation hearing in January. Price confronted accusations
of investing in companies related to his legislative work in Congress -- and in some cases, repealing financial benefits from those investments. Price firmly denied any wrongdoing and insisted that he has taken steps to avoid any conflicts of interests.
Trump watches as Pence administers the oath of office to Attorney General Jeff Sessions in the White House Oval Office on Thursday, February 9. Sessions, one of Trump's closest advisers and his earliest supporter in the Senate, was confirmed by a 52-47 vote
that was mostly along party lines. He was accompanied to the swearing-in by his wife, Mary.
In his wide-ranging confirmation hearing,
Sessions pledged to recuse himself from all investigations involving Hillary Clinton based on inflammatory comments he made during a "contentious" campaign season. He also defended his views of the Supreme Court's Roe v. Wade ruling on abortion, saying he doesn't agree with it but would respect it.
Pence swears in Education Secretary Betsy DeVos next to her husband, Dick, on Tuesday, February 7. Pence cast a historic tie-breaking vote
to confirm DeVos after the Senate was divided 50-50.
DeVos, a top Republican donor and school-choice activist,
prepares to testify at her confirmation hearing in January. DeVos stood firm in her long-held beliefs
that parents -- not the government -- should be able to choose where to send children to school, pledging to push voucher programs if she was confirmed.
Trump watches as Pence swears in Rex Tillerson as secretary of state on Wednesday, February 1. Tillerson's wife, Renda St. Clair, holds the Bible. Tillerson, a former CEO of ExxonMobil, was confirmed in the Senate
by a vote of 56 to 43.
Elaine Chao, Trump's pick for transportation secretary, signs the affidavit of appointment during her swearing-in ceremony in Washington on Tuesday, January 31. Chao is joined, from left, by Pence; her father, James Chao; and her husband, Senate Majority Leader Mitch McConnell.
Chao testifies at her confirmation hearing
in January. Chao, who was approved by a 93-6 vote, was deputy secretary of transportation under George H.W. Bush and labor secretary under George W. Bush.
South Carolina Gov. Nikki Haley takes the oath of office as she becomes the US Ambassador to the United Nations on Wednesday, January 25. She is joined by US Sen. Marco Rubio and staffer Rebecca Schimsa as she is sworn in by the vice president.
During her confirmation hearing,
Haley rapped the UN for its treatment of Israel and indicated that she thinks the US should reconsider its contribution of 22% of the annual budget. "The UN and its specialized agencies have had numerous successes," Haley said. "However, any honest assessment also finds an institution that is often at odds with American national interests and American taxpayers. ... I will take an outsider's look at the institution."
Mike Pompeo is joined by his wife, Susan, as he is sworn in as CIA director on Monday, January 23. Pompeo, who is vacating his seat in the US House, was confirmed by the Senate
in a 66-32 vote.
Pompeo is sworn in at his confirmation hearing.
Along with Russia, Pompeo said other global threats include Iran's growing influence in the Middle East, ISIS' grip over major urban areas, and the conflict in Syria.
Mattis testifies before the Senate Armed Services Committee. He emerged from his confirmation hearing
with broad support after he took a strong posture against Russian President Vladimir Putin and answered tough questions on women and gays in combat.
Retired Marine Gen. John Kelly signs his confirmation letter on January 20. He is joined by his wife, Karen.
Kelly testifies at his hearing.
He was previously the head of US Southern Command, which is responsible for all military activities in South America and Central America.
"They did not discuss anything having to do with the United States' decision to expel diplomats or impose censure against Russia," Pence told CBS News.
On Friday, an aide close to the national security adviser told CNN that Flynn could not rule out that he spoke about sanctions on the call.
The White House official blamed much of the outcry against Flynn on a Washington culture always in search of a scalp, but people within Trump's orbit did little to defend Flynn during appearances on Sunday news shows.
Stephen Miller, White House policy director, was asked directly about Flynn's future on a number of Sunday talk shows. Miller responded by saying he was not the appropriate official to ask.
"I don't have any answers today," Miller said in response to questions about whether Flynn misled the vice president. "I don't have any information one way or another to add anything to the conversation."
CNN's Jim Acosta, Kevin Liptak and Dan Merica contributed to this report.