WATCH: Sally Yates Testifies: 'We Believed Gen. Flynn Was Compromised'

It was a matter of urgency, former acting Attorney General Sally Yates says, when she called White House lawyers back in late January.

She needed to tell them that Gen. Michael Flynn, then-national security adviser, appeared to be lying to the White House, making him vulnerable to blackmail by Moscow.

"We believed that Gen. Flynn was compromised with respect to the Russians," Yates told a Senate subcommittee on Monday. "To state the obvious, you don't want your national security adviser compromised by the Russians."

Four days later, Yates was fired, for refusing to defend President Trump's travel ban.

Two weeks after that, Flynn was out — for lying to the White House about contacts with Russia, as Yates had alerted White House lawyers. The story Yates had warned about had reached the press.

Yates, along with James Clapper, former director of national intelligence, appeared before the Senate Judiciary Committee's crime and terrorism subcommittee to testify on Russian attempts to interfere in the U.S. presidential election.

Both witnesses had served under Obama. Yates remained in her role for 10 days after Trump's inauguration on Jan. 20 and then was fired.

During that brief tenure she warned the White House that Flynn had made contact with Russians, which he was denying. Vice President Pence was publicly backing Flynn's false statements.

Yates told the senators she informed the administration about Flynn's apparent lie for two reasons: one, because Flynn's behavior was "problematic in and of itself," and two, because she believed Pence had "the right to know" the truth. She said she was sharing the information — over a series of two meetings and a phone call — so that the White House "could act."

In response, she says, one lawyer asked what it mattered to the Department of Justice if one White House official was lying to another.

The senators in Monday's hearing asked about issues beyond just Flynn. But many of the highest-stake questions in the hearing ran up against a brick wall marked "classified."

Clapper said he could not comment on whether he was concerned about Trump's business interests in Russia. And as to whether there's evidence that members of the Trump campaign cooperated in Russian meddling, they were split: Clapper said he didn't know of any, while Yates said she couldn't comment.

At the hearing on Monday — as at previous public hearings on the Russian investigation — there was a sharp partisan split in how senators approached the issue.

Democrats focused extensively on Russian attempts to alter the outcome of the U.S. presidential election in Trump's favor, while most Republicans focused on leaks and the question of how Flynn's calls reached the press. (Both Yates and Clapper flatly denied having any involvement with the leaks.)

Some Republican senators even turned their attention to Hillary Clinton's emails and Yates' refusal to defend Trump's executive order on travel.

The president tweeted after the hearing, calling congressional investigations into the possibility that his campaign colluded with Russia a "taxpayer funded charade."

He said the "biggest story," which he accused the media of underreporting, is "on surveillance." Questions about what kind of surveillance it is legal for U.S. intelligence agencies to do, and whether intelligence from such surveillance has been mishandled, did come up during the hearing and have been reported on extensively for the past few months.

You can read about the hearing, as it happened, below, and watch video here.

5:30 p.m. ET: Both witnesses call for defensive action against future meddling

Asked about what needs to be done to defend against future Russian actions, Yates said, "I think they're coming back ... and I think we have to do a whole lot more — to harden our election systems, to ensure that folks out there know when they're looking at news feeds that it may not be real news that they're reading.

"I think that we have to do more to deter the Russians, and it wouldn't hurt to prosecute a few folks, but I don't think we can fool ourselves that we can prosecute our way out of this problem," she said.

"I think the most important thing we need to do here is to educate the electorate ... about Russian tactics and procedures, that they have employed and I predict will continue to employ," Clapper said.

He also said U.S. election systems should be considered critical infrastructure and called for more sanctions and improved countermessaging against Russia.

5:15 p.m. ET: Clapper declines to comment on Trump's business interests in Russia

Subcommittee Chairman Lindsey Graham, R-S.C., asked Clapper if he had, in the course of investigations, come across business ties Trump had to Russia that caused concern. There was a pause, then this exchange:

Clapper: Not in the course of the preparation of the intelligence community assessment.

Graham: Since? ... At all? Anytime?

Clapper: Sen. Graham, I can't comment on that, because that impacts an investigation.

Graham: It wasn't enough to put into the report?

Clapper: That's correct.

5:10 p.m. ET: Questions about Flynn's security clearance

At a news conference earlier Monday, White House press secretary Sean Spicer said that Flynn received a security clearance during his time with the Obama administration and that it was never withdrawn. He had the "same clearance" as national security adviser, Spicer said.

"Everyone in the government goes through the same process," Spicer said. As for vetting Flynn, Spicer said, "That was something that was adjudicated by the Obama administration."

Sen. Mazie Hirono, D-Hawaii, asked Clapper whether that was true. Clapper said he couldn't comment on Flynn specifically — but that there are very different levels of vetting for different roles.

"I know what I went through as a political appointee, twice, in a Republican and Democratic administration, and the vetting process for either a political appointee or someone working with the White House is far more invasive and far, far more thorough than a standard TS/SCI clearance process," Clapper said. "But I don't know what process was used in Gen. Flynn's case."

He reiterated later that serving in a high-level role in the White House has, in previous administrations, required vetting above and beyond a standard security clearance.

NBC has reported that Flynn was required to get a new security clearance to serve as national security adviser, but the process was never completed; he was pushed out of the job before he received that higher clearance, NBC reported, citing one anonymous source.

5:05 p.m. ET: Yates won't confirm whether Flynn lied to the FBI

Yates said she couldn't comment on whether Flynn lied during his interview with the FBI, citing an ongoing investigation.

She did confirm that if Flynn did lie, he could potentially face criminal prosecution.

5:00 p.m. ET: Al Franken poses a lengthy hypothetical

Sen. Al Franken, D-Minn., used one of his questions to, well, not really ask a question. He was talking to Yates about the 18-day delay between when she alerted the White House to Flynn's apparent lie, and when Flynn was forced to resign:

"Is it possible that the reason he didn't fire him then is that [he thought], 'Well, if I fire him for talking to the Russians about sanctions ... what about all the other people on my team who coordinated?'

"You ask yourself, why wouldn't you fire a guy who did this. And all I can think of is that he would say, 'Well, we've got all these other people in the administration who have had contacts; we've had all these other people in the administration who coordinated.' ...

"We're trying to put a puzzle together here, everybody, and maybe, just maybe, he didn't get rid of a guy who lied to the vice president, who got paid by the Russians, who went on Russia Today, because there are other people in his administration who met secretly with the Russians and didn't reveal it until later, until they were caught. That may be why it took him 18 days — until it became public — to get rid of Mike Flynn, who was a danger to this republic."

"Care to comment?" Franken asked Yates.

"I don't think I'm going to touch that, senator," she said.

4:25 p.m. ET: Russian hacking is cheap; does WikiLeaks do journalism?

Sen. Ben Sasse, R-Neb., asked Clapper about the threat from Russia — among other things, whether congressional IT systems could be a target of hacking, which Clapper said was certainly possible. He also asked about how much money Russia spends on hacking and propaganda efforts.

"I can't give you a figure," Clapper said. "I will say in comparison to classical military expenditures it's a bargain for them."

Then Sasse raised the question of WikiLeaks, as he did with FBI Director James Comey last week. He asked whether the group is a "known propaganda effort for Russia," as U.S intelligence officials have called it.

He asked Clapper, "You're saying that Julian Assange is not a journalist?"

"You're asking the wrong guy," Clapper said, laughing. "He certainly is not."

"When a journalist does harm to the country, harm to our national security, compromises sensitive sources ... and deliberately puts the country in jeopardy, I think that's a red line," Clapper said.

4:15 p.m. ET: Yates repeats her goal was to allow White House to "take action" regarding Flynn

In her answers to the senators, Yates has repeatedly emphasized that she was briefing White House lawyers on Flynn's behavior so that the administration "could take action."

She says the Department of Justice was "very concerned" and that in conversations with the White House, she emphasized "repeatedly" that they were sharing the information to enable the administration to act.

3:55 p.m. ET: Conversation pivots to Trump's travel ban, Clinton's emails

In a diversion from the topic at hand, Sen. John Cornyn, R-Texas, challenged Yates over her decision not to defend Trump's travel ban.

That prompted Sen. Dick Durbin, D-Ill., to defend Yates — and then express frustration with the Senate subcommittee's lack of resources dedicated to the question at the heart of the hearing, that is, Russian meddling in the election.

Sen. Ted Cruz, R-Texas, then asked "hypothetical" questions about Hillary Clinton's emails, as well as further questions about Trump's executive order on travel.

As the conversations about the travel ban continued, Yates confirmed that she met with White House counsel — to discuss Flynn — on the same afternoon that the White House was preparing to issue the executive order on immigration.

They did not tell her of the plans, she said: As acting attorney general she learned about the order after it was issued, from media coverage.

3:45 p.m. ET: Yates says it "certainly appeared" that Flynn lied

Yates told the senators the Department of Justice had two concerns over Flynn's actions. One was that he could be vulnerable to blackmail by Russia.

"Compromise was certainly the No. 1 concern," she said. "The Russians can use compromised material in a variety of ways, sometimes overtly, sometime subtly, and again our concern was that you have a very sensitive position — like the national security adviser — and you don't want that person to be in a position where the Russians have leverage."

But they also felt that Pence had the "right to know" that evidence contradicted the statements he was making, as he defended Flynn in public.

Asked if Flynn lied to Pence, Yates said, "That's certainly how it appeared, yes — because the vice president went out and made statements that he said were based on what Gen. Flynn had told him," and which the DOJ knew "flatly" weren't true, Yates said.

3:15 p.m. ET: Yates says she told the White House multiple times that Flynn's conduct was "problematic"

Yates says she spoke with White House counsel twice in person, and once over the phone, about Flynn's "conduct."

She wouldn't detail what the conduct was, saying that was classified, but identified it as "problematic in and of itself."

The first meeting was on Jan. 26, when Yates told the White House that there was evidence of Flynn's conduct that contradicted public statements by Vice President Pence. Yates says she was not accusing Pence of "providing false information" but wanted to make sure the White House was aware of the disparity.

Yates also says she informed the White House that Flynn had been interviewed by the FBI, but without specifying what happened in that interview.

It was a matter of urgency, Yates said.

"We believed that Gen. Flynn was compromised with respect to the Russians," Yates said. "... To state the obvious, you don't want your national security adviser compromised by the Russians."

But she says the Department of Justice, despite feeling this sense of urgency, was also trying not to interfere in an active FBI investigation.

Flynn was forced to resign as national security adviser 18 days after Yates met with White House lawyers.

3:10 p.m. ET: Clapper, Yates both say they don't know how Flynn's conversations reached the press

Graham asked Yates and Clapper how the White House learned that Flynn had conversations with the Russian ambassador.

That's a question that President Trump had called for the senators to ask — in line with Republican allegations that an Obama official leaked classified information about Flynn.

Both witnesses said they did not know the answer. Later, both denied serving as an anonymous source, or authorizing anyone else to serve as an anonymous source, in connection with the story.

3:10 p.m. ET: Yates says she can't comment on possibility of Trump campaign collusion

Yates refused to say whether intelligence exists that shows a member of the Trump campaign colluded with the Kremlin.

"My answer to that question would require me to reveal classified information," Yates said.

But she urged the senators not to take that nonanswer as confirmation that evidence does exist, saying she was taking the same approach as FBI Director James Comey to a question that centers on a classified investigation.

Clapper had a different answer to the question, saying flatly that he did not know of any evidence.

Further pressing by the senators raised the point that it was at least possible for individuals with the Department of Justice to have access to information that Clapper, as director of national intelligence, did not — because of the high level of secrecy around counterintelligence investigations.

2:55 p.m. ET: Clapper pushes back on concerns over unmasking

Graham, in his opening remarks, raised unmasking as a major area of concern.

"Unmasking" is how American officials can learn the names of Americans caught up in "incidental collection" — that is, people overheard or mentioned as the U.S. is surveilling a foreign target. (You can read more about both concepts in our background material above.)

Some Republicans have expressed concern that Flynn may have been "unmasked," and then his identity leaked to the press, for political purposes instead of for legitimate intelligence reasons.

"I've learned a bit about unmasking and what I've learned is disturbing," Graham said. "I'd like to know more and I want to make sure that that unmasking can never be used as a political weapon in our democracy."

Clapper explained that an official asking for unmasking has to justify why the name is needed and that the name is shared only with the person requesting it. Clapper said he had personally requested unmasking several times.

"At no time did I ever submit a request for personal or political purposes, or to voyeuristically look at raw intelligence, nor am I aware of any instance of such abuse by anyone else," Clapper wrote.

2:45 p.m. ET: Witnesses warn that their testimony is constrained

As he opened the hearing, Graham noted that the U.S. intelligence community has been "unanimous" in concluding that Russia was meddling in the U.S. election.

While Russian hacking and propaganda was designed to help Trump and hurt Hillary Clinton, Graham said, such foreign interference is a bipartisan issue.

"It could be our campaigns next," he told his fellow senators. "When one party is attacked, all of us should feel an attack."

The subcommittee's ranking member, Sheldon Whitehouse, D-R.I., went into much greater detail about what Russia is known or believed to have done to influence the U.S. election.

"We need a more thorough accounting of the facts," Whitehouse said.

Meanwhile, Yates and Clapper both warned the subcommittee that they won't be able to answer pressing questions as fully as the senators might like.

"Many of the topics of interest today concern classified information that I cannot address in this public setting, either directly or indirectly," Yates wrote in her statement, published on Graham's website.

She also said she is "not authorized" to discuss deliberations within the Department of Justice or the executive branch, "particularly on matters that may be the subject of ongoing investigations."

Clapper, for his part, said the White House cited executive privilege and "requested" additional limits to what he can discuss in the hearing.

2:30 p.m. ET:

NPR's Phil Ewing provides a preview of what's expected to be discussed:

"Democrats want Yates to describe what she told White House officials shortly after President Trump's inauguration about the FBI's investigation into then-national security adviser Michael Flynn. Yates' Jan. 26 meeting in the executive mansion reportedly was to notify the administration that the FBI believed Flynn could be vulnerable to Russian blackmail. He resigned weeks later. ...

"Graham and Republicans, however, want to ask the witnesses about how details of Flynn's conversations, and other classified information, found their way into The Washington Post and other newspapers ahead of Trump's inauguration."

Trump had been cautioned about Flynn even before the heads-up from Yates on Jan. 26, according to a former Obama official. The official tells NPR that the president himself warned Trump, then incoming president, about Flynn's job performance.

Flynn was formerly the head of the Defense Intelligence Agency but was fired during the Obama administration.

White House press secretary Sean Spicer confirmed on Monday that "President Obama made it clear that he was not a fan of Gen. Flynn's." But Spicer suggested that wasn't surprising — given Flynn's criticisms of Obama — and could have been interpreted as "bad blood" instead of a substantive warning.

"If President Obama was truly concerned, why didn't he suspend Gen. Flynn's security clearance?" Spicer asked.

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