Here are the top five things we learned from their appearance before the Senate Judiciary Committee's Subcommittee on Crime and Terrorism on Monday:
As soon as she read the details of Michael Flynn's interview with the FBI, at the end of January, Yates called White House counsel Don McGahn and said they needed to talk in private, she testified.
Yates brought one of her top staffers with her on the afternoon of January 26 to meet with McGahn and one of his top aides inside a secure facility on the White House grounds so they could discuss the FBI's interview of Flynn. It was then, she testified before senators Monday, that she warned McGahn that President Donald Trump's national security adviser could easily become a blackmail target for Russians, based on the answers Flynn gave to the FBI.
"That created a compromised situation, a situation where the national security adviser essentially could be blackmailed by the Russians. Finally, we told them that we were giving them all of this information so that they could take action, the action that they deemed appropriate," she said. McGahn called Yates and asked her to return the next morning, January 27, when she testified that he asked her about four main concerns:
- Why did it matter to the Justice Department if Flynn lied to Vice President Mike Pence?
- What criminal statutes did Flynn potentially violate?
- Would taking action against Flynn immediately interfere with the FBI's investigation?
- Could he see the underlying evidence collected in Flynn's interview?
Yates explained that any official publicly repeating the lie that Flynn had not discussed sanctions with Russian ambassador to the US, Sergey Kislyak, was increasing the chance Flynn would be blackmailed.
"Every time this lie was repeated and the misrepresentations were getting more and more specific, as they were coming out, every time that happened, it increased the compromise and to state the obvious: You don't want your national security adviser compromised with the Russians," Yates said.
Flynn's lawyer, Robert Kelner, declined comment when reached by CNN Monday.
2. Trump is increasingly looking alone in his belief that Russia did not interfere to help him in the 2016 election
Trump has repeatedly called the investigations of possible coordination between his campaign aides and Russia "fake news" and, last week, said it may have been China that was behind the hacking.
That's an assessment that's looking increasingly detached from US intelligence officials.
"To me, the evidence was overwhelming, and very compelling, that the Russians did this," Clapper testified, when asked about Trump's most recent assertions.
Then, prompted by Democratic Sen. Patrick Leahy, Clapper said Trump may still be helping the Russians by denying their involvement.
"You could rationalize that it helps the Russians by obfuscating who was actually responsible," Clapper said.
3. Clapper and Yates undercut one of the Trump White House's strongest arguments
Throughout the Russia probes, the Trump White House has pointed to testimony earlier this year from Clapper that he had seen no evidence in the January intelligence report of collusion between the President's campaign and Russia. That was before FBI Director James Comey publicly revealed that the FBI was, in fact, investigating that question.
Clapper said Comey's March 20 testimony was the first he heard of the FBI investigation. He later said that his original assessment was that there was no evidence he had seen worth including in the intelligence assessment -- but Yates later said that she could not answer the question because she did not want to reveal any classified information.
The implication from both officials' testimonies was that there may, indeed, be evidence of collusion -- this after months of the White House arguing that Clapper was clear there is no evidence.
4. The Senate investigations have strong strains of partisanship
Monday's hearing with Yates and Clapper was clearly focused on Russia's interference in the 2016 election, but Republican and Democratic senators still used it to land some partisan shots.
Republican senators grilled Yates on why she refused to enforce the first executive order that imposed a travel ban issued by Trump.
"I don't mean any disrespect: Who appointed you to the Supreme Court?" Sen. John Kennedy, a Louisiana Republican, told Yates in a comment that immediately lit up Twitter.
And Texas GOP Sen. Ted Cruz went to town on Yates, arguing that she may have broken the law by refusing to defend the order. She rebutted him by pointing to a later court ruling that supported her argument that she had a greater duty to protect against discrimination and uphold the Constitution.
Democrats, meanwhile, pushed hard with lines of attack clearly aimed at damaging Trump himself, not necessarily digging into what happened in the 2016 elections.
Connecticut Sen. Richard Blumenthal, one of the Senate's most staunchly liberal members, took Yates on a winding line of questioning that ended with Trump possibly appearing on the witness stand in a hypothetical court trial against Flynn. At the end of the hypothetical exercise, Blumenthal pressed Yates if that was even remotely possible.
Yates responded: "Potentially."
The Senate Russia investigators may have maintained the air of being the adults in Congress investigating Russia's interference. But the Senate Judiciary Committee has proved over the last two hearings (including last week's with Comey) that partisanship is still a powerful force in its own inquiry.
5. The media matters
Yates was fired by Trump one day after it came out that she had refused to defend his travel ban and four days after she first alerted McGahn about Flynn. Meanwhile, it took 18 days for the White House to fire Flynn after Yates first told McGahn about his FBI interview.
"Without that published report, and without the free press telling us a lot of what went on, Michael Flynn might still be sitting in the White House as national security adviser," said Blumenthal, referring to the original Washington Post report
about Flynn's phone calls with Kislyak.