National security adviser Mike Flynn resigned Monday night following a furor concerning his ties to Russian officials.

The sudden resignation came after multiple news reports said Monday that the Justice Department had warned the White House weeks ago that Flynn had misled them concerning his contacts with Russia and could be compromised.

The Washington Post reported that acting Attorney General Janet Yates told White House counsel Donald McGahn last month that Flynn had misled them on the extent of his contacts with the Russian ambassador and that he was vulnerable to blackmail. Then-national intelligence director James Clapper and then-CIA chief John Brennan agreed with Yates, fearing “Flynn had put himself in a compromising position,” the Post reported.

The Associated Press,New York Times and Wall Street Journal also reported the Justice Department’s warnings Monday. It is unclear what, if anything, McGahn did with the information. Yates was fired Jan. 30 after refusing to defend President Donald Trump’s temporary immigration ban.

Flynn reportedly had a number of phone calls with Russia’s ambassador to the U.S., Sergey Kislyak, both before and after Trump’s November election victory. Flynn, the White House and Vice President Mike Pence all publicly denied that Flynn discussed easing recent U.S. sanctions against Russia in those conversations, but Flynn has recently admitted that the subject may have come up before Trump’s inauguration. If so, such conversations could have been illegal.

“Unfortunately, because of the fast pace of events, 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 said in his resignation letter.

Just hours earlier, senior Trump adviser Kellyanne Conway said Trump still had “full confidence” in Flynn, though press secretary Sean Spicer later said the White House was “evaluating” his status. Trump has not commented on Flynn in recent days.

Flynn had been one of Trump’s earliest supporters, and ended up serving just 24 days in his administration. Trump named retired Gen. Keith Kellogg acting national security adviser late Monday.

Flynn’s resignation is unlikely to end the controversy. House Democrats had called for an investigation into Flynn’s Russian contacts, and will almost certainly pursue that.