Though Yates would not discuss classified details of the Flynn matter, other people familiar with the matter said the issue she raised to McGahn were conversations between Flynn and Russian ambassador Sergey Kislyak, in which the two discussed easing USA sanctions against Russia.
But the Congressional hearing into allegations of Russia's meddling in last year's United States presidential elections, which began on Monday, have focused on Flynn, and if the charges against the former army lieutenant are proven, it would seriously cripple Trump's case in Congress.
As soon as she read the details of Michael Flynn's interview with the Federal Bureau of Investigation, at the end of January, Yates called White House counsel Don McGahn and said they needed to talk in private, she testified.
Flynn was interviewed by the Federal Bureau of Investigation in the early days of the Trump administration about communications he had with Kislyak, the Russian ambassador to the United States, during the transition period.
"Logic would tell you that you don't want the national security adviser to be in a position where the Russians have leverage over him", she added.
Later on Monday, former acting attorney general Sally Yates, an Obama appointee sacked by Trump early in his presidency, took the stand alongside former director of national intelligence James Clapper during a hotly-anticipated three-hour hearing of the Senate Judiciary Committee.More news: NBCSN Senators vs. Rangers Game 3 Hockey 5pm CT
Yates said she expected Flynn to be removed quickly by the White House, but the decision to dismiss him came more than two weeks later, after The Washington Post revealed he had lied to Pence about speaking with a Russian ambassador. She was joined in the meeting by a senior career official in the Justice Department.
"We weren't the only ones that knew all of this", said Yates. "And that created a compromise situation, a situation where the national security adviser essentially could be blackmailed by the Russians".
Despite these claims, however, Trump has stood his ground, saying the information is not new news, and his administration has effectively purged the wrongdoers. He testified that he did not know about the FBI investigation into Russian meddling in the election and whether there were any links to the Trump campaign until its existence was announced in a congressional hearing by FBI Director James Comey in March.
Yates testified that she told a senior administration official in January that Flynn had been "compromised" and that she suspected Russian Federation knew Flynn had misled Vice President Mike Pence.
While Trump can afford to be belligerent at the moment, it remains to be seen for how long he can maintain his cool, if allegations against Flynn keep piling up.
She explained to McGahn the reasons why the DOJ was informing the White House of this - Flynn's conduct was "problematic in and of itself", they believed Pence was entitled to know the information about Flynn he was spreading "wasn't true", and that the American people had been misled about Flynn's actions.More news: Ryan Seacrest is Kelly Ripa's new co-host on 'Live'
Yates left her post with the DOJ that day because Trump fired her after she ordered the Justice Department not to defend Trump's January 27 executive order.
And each time that White House officials repeated misrepresentations of Flynn's actions, Yates argued it "increased the compromise".
Mr Trump has repeatedly said he has no ties to Moscow and is not aware of any involvement by his aides in any Russian interference in the election. And that's been part of the discussion with the courts with respect to the INA is whether this more specific statue trumps the first one that you just described. Rice has said she did nothing improper. In the days before the originally scheduled hearing, Yates' attorney, David O'Neil, had been locked in an argument with Trump administration officials about whether she would be barred by executive privilege from testifying about her conversation with McGahn.
A week before the planned House hearing, O'Neil went to the Justice Department to discuss the issue of her testimony.
Yates' second in-person meeting with McGahn happened the next day. As O'Neil awaited a response from the White House, Nunes canceled the hearing, making the legal issue moot.More news: Fury: I can beat AJ with one arm tied behind my back
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