Trump has provided no evidence to support the claim, and Yates said under oath that Obama’s only interest in Flynn was to ensure that it was safe to share sensitive national security information with the incoming administration while the FBI was probing concerns that Flynn was attempting to undermine sanctions leveled by Obama in response to Russia’s interference in the 2016 election.

“General Flynn had essentially neutered the U.S. government’s message of deterrence,” Yates said.

Flynn pleaded guilty in 2017 to lying to the FBI about those efforts, which he made during a series of phone calls, weeks before Trump’s inauguration, with Russia’s then-U.S. Ambassador Sergey Kislyak. Transcripts of those calls show that Flynn urged Russia not to escalate in response to the Obama administration sanctions, and that Kislyak later told him Vladimir Putin refrained from retaliation because of his request.

Yates also rejected assertions that a discussion of a potential violation by Flynn of the Logan Act — a largely obsolete 18th-century law intended to prevent private citizens from interfering in foreign policy — was a central focus of the FBI’s reason for pursuing its Flynn investigation. Rather, she said, Flynn’s conversations with Kislyak and subsequent lies about those calls both publicly and to FBI agents investigating Russia’s efforts, were an obvious counterintelligence risk.

The Logan Act “wasn’t our primary concern,” she said. “It was a counterintelligence concern.”

Yates’ appearance before the Judiciary Committee, part of Chairman Lindsey Graham’s investigation into the origins of the FBI’s investigation of the Trump campaign’s links to Russia in 2016, is part of an effort by Trump allies to undercut the basis for the probe, which they say was a politically motivated effort to amplify charges of collusion between Trump and Russia.

But the hearing also offered Yates a chance to repeatedly knock down allegations of misconduct and incorrect assertions about the Obama administration’s actions in the closing days of the administration. Yates corrected Graham for incorrectly asserting that the FBI had closed its case on Flynn before it interviewed him on Jan. 24, 2017. She also called it highly irregular that the Justice Department recently dropped the case against Flynn, who reversed course and sought to withdraw his guilty plea earlier this year.

And Yates also emphasized that there was no effort to monitor Flynn’s communications. Though she said DOJ didn’t permit her to share exactly how the FBI obtained a recording of Flynn’s calls with Kislyak, monitoring of foreign operatives like Kislyak on U.S. soil is a routine practice.

“There was no surveillance of General Flynn,” Yates said.

Republicans focused much of their questioning on Yates' October 2016 approval of an application to surveil former Trump campaign aide Carter Page, who the FBI suspected of acting as a Russian agent. The application relied heavily on a dossier compiled by former British intelligence official Christopher Steele, who was collecting anti-Trump information for a company hired by the Clinton campaign and Democratic Party.

The so-called Steele dossier's reliability has been undercut in the years since, and Republicans have accused the FBI of leaning on the opposition research document to justify monitoring Page. In addition, a review by inspector general Michael Horowitz found that the application included a slew of errors and omissions, though he did not find the application itself to be invalid.

Yates insisted that she rigorously reviewed the application but relied, as is required, on the factual representations made by the FBI to determine whether to approve it. She acknowledged that the Steel Dossier was an important component of the application and emphasized that anyone who participated in making false representations to the court that approved the warrant for Page should be held accountable.

Yates emphasized that despite the problems with the FISA application, Horowitz did not find evidence that political bias was a contributing factor and in fact did not include the political provenance of the Steele Dossier as one of the errors he found with the FBI's process. Yates indicated she had internal discussions about potential political motivations behind the dossier with a lawyer in her office but added, "I was not aware the DNC was funding it."

Graham said he intends to steer his committee's continuing investigation toward the FBI agents and analysts who interviewed Steele's primary source of information, a researcher whose identity was recently revealed after Graham released a redacted summary of the source's FBI interview, declassified last month by the Justice Department. As the hearing wound down, Graham indicated that the summary he released was actually the first of three with Steele's source and that he intends to interview "the intel analyst and case agent and two others."

"We're going to ask them, 'Oh by the way, did you tell anyone in the FBI that the reliability of the dossier has gone down to zero.' And if you did tell somebody, who was it?" Graham said. "Then we'll decide as a nation what accountability they should have, whether it be being fired, going to jail or whatever. That is the purpose of this investigation going forward."

Graham (R-S.C.) said at the outset of the hearing that he considered the FBI’s rationale for interviewing Flynn to be a “sham.”

“We need to make sure going forward in the next transition, no matter who wins, that you can talk with foreign leaders without being afraid of going to jail,” Graham said.

Despite sharp questioning at times, Graham offered repeated praise for Yates, whom he said resisted some of the most controversial decisions made by the FBI during the outgoing days of the Obama administration. But his plaudits were quickly undercut by Trump, who contradicted Graham with a tweet in the early moments of the hearing.

“Sally Yates has zero credibility. She was a part of the greatest political crime of the Century, and ObamaBiden knew EVERYTHING!” Trump said, reviving an attack on his predecessor that he’s provided no evidence to support.

Trump also urged Republicans to press Yates on whether she was the source of a classified leak of a conversation between Flynn and Kislyak, which helped drive a public furor in the days leading up to Trump’s inauguration.

“Ask her under oath,” Trump said. “Republicans should start playing the Democrats game!”

No senators asked Yates about the leak, though she has previously denied being the source.

When Sen. John Kennedy (R-La.) asserted that Yates didn't like Trump, she replied, "I don’t respect the manner in which he has carried out the presidency."

Kennedy pressed: "You despise Trump."

"I don't despise anyone," Yates said.