Days before she was fired as acting attorney general, Sally Yates told a Senate panel Monday that she was so troubled that former National Security Adviser Michael Flynn had misled Vice President Mike Pence about his communications with the Russian ambassador that she met twice at the White House to discuss Flynn’s possible vulnerability to blackmail and exposure to criminal charges.

For the first time publicly, Yates recounted to a Senate panel a Jan. 26 meeting – and a follow up session the next day – in which she alerted White House Counsel Don McGahn that Flynn had lied to administration officials about his conversations with Russian ambassador Sergey Kislyak before Trump's inauguration, prompting McGahn to ask whether Flynn should be dismissed.

Yates said she offered no opinion on Flynn's continuing service, but conveyed the "urgent'' nature of her concerns.

"You don’t want a situation where a national security adviser could get blackmailed by the Russians,’’ Yates told a Senate Judiciary subcommittee.

Flynn's contacts with the ambassador, according to officials who have previously described the communications, involved discussions with the ambassador about sanctions imposed on Russia by the Obama administration. Those conversations were secretly monitored by federal authorities, as are most communications involving foreign diplomats.

Pence, for his part, had said he had been assured by Flynn that the subject of sanctions was not raised in the Kislyak conversations.

Yates, citing the classified nature of how the communications were obtained, declined to elaborate on the intercepts. But she said the anxiety about Flynn's actions was so great within the Justice Department that members of its national security division were consulted, as were other intelligence officials across the government.

"Compromise was the No. 1 concern,'' Yates, referring to the possibility that Russian officials, aware that Flynn had misled the White House, could blackmail him by threatening his career.

"It was a whole lot more than one White House official lying to another,'' Yates said. "It involved the vice president of the United States.''

Shortly after Yates' warnings were made public, Flynn was forced to resign, ending the shortest tenure of any president's national security adviser – while stoking further suspicion about the ties between Trump associates and Russian officials.

Four days after Yates' first meeting with the White House counsel, President Trump fired the career federal prosecutor for her actions on a separate matter. A holdover from the Obama administration, Yates had instructed Justice lawyers not to defend Trump's travel ban.

Some Republicans seized on that decision Monday, including Texas Sen. Ted Cruz, suggesting that her actions were partisan. But Yates defended the directive, saying that there were “constitutional concerns’’ about the language of the order and that she was “not convinced that the it was lawful.”

Yates also claimed that Justice’s Office of Legal Counsel, which had previously approved Trump’s order, was specifically instructed not share their deliberations with the interim Justice leadership before the travel ban was made public.

The specter of Yates' testimony was not lost on Trump, who early Monday fired off two tweets distancing the administration from Flynn while suggesting that Yates may have leaked information about her actions related to the former national security adviser.

"General Flynn was given the highest security clearance by the Obama Administration - but the Fake News seldom likes talking about that,'' Trump said. "Ask Sally Yates, under oath, if she knows how classified information got into the newspapers soon after she explained it to W.H. Council (sic).''

Trump and Obama administration officials also confirmed Monday that Obama advised Trump not to hire Flynn during their post-election White House meeting.

Since then, Flynn and former Trump advisers, including Carter Page, Paul Manafort and Roger Stone have become the subjects of fresh scrutiny about their Russian ties.

​On Saturday, the Washington Post reported that Trump transition team members had warned Flynn about the risks of communicating with the Russian ambassador, prior to the his December telephone conversations with Kislyak. According to the report, Flynn was told in November that the ambassador's communications were likely being monitored by U.S. authorities.

Separately, the Senate Intelligence Committee, which along with the House Intelligence Committee are conducting a parallel inquiries into Russian interference in the 2016 elections, recently asked the advisers to provide information about their activities.

Flynn also is now under investigation by the Pentagon Inspector General for failing to inform Defense Department officials about seeking payments from foreign governments.

Sen. Lindsey Graham, R-S.C., who is leading Monday's Senate Judiciary subcommittee hearing, has said the panel's examination is necessary to "hold [Russia] accountable.''

"Based on evidence presented by our intelligence and law enforcement communities, I believe Russia interfered in our election,'' Graham has said. "I do not believe it changed the outcome, but I have no doubt they interfered.'' The U.S. intelligence community has accused Moscow of orchestrating a campaign of cyberattacks to hack Democratic political organizations and release stolen information to undermine confidence in the American election.

It is not immediately clear how much new information Yates and former Director of National Intelligence James Clapper, who also is scheduled to testify Monday, will be able provide. Both witnesses are constrained by the classified nature of the information surrounding the events they were privy to.

In March, when Yates' attorney had notified the Justice Department and White House of her intent to appear at a previously scheduled House Intelligence Committee hearing, the attorney was warned that Yates' testimony could contained privileged communications that might be barred.

Ultimately, Yates' scheduled March 28 appearance was canceled.

Trump spokesman Sean Spicer has since indicated that the White House has no objection to Yates' testifying. And last week , Graham signaled that senators will ask Yates about what other possible considerations drove her to alert the White House counsel about her concerns for Flynn.

Responding to a series of questions from Graham, FBI Director James Comey recalled in separate testimony last Wednesday before the Senate Judiciary Committee that he met with Yates to discuss her concerns about Flynn's activities. The meeting occurred after FBI agents interviewed Flynn about his conversations with the Russian ambassador.

Comey declined to elaborate on the meeting with Yates in the open committee session.

Attorneys for Yates and Flynn did not respond to inquiries seeking comment.

Flynn, meanwhile, has sought immunity from any possible prosecution. Both the House and Senate Intelligence committees, in the midst of continuing Russia probes, have indicated that it is too early in their investigations to cut a deal for Flynn's testimony. Separately, preliminary discussions about Flynn's prospects for immunity in the FBI investigation also have yielded no agreement.