Former official says she warned White House about Flynn

"The Russians also knew about what General Flynn had done, and the Russians also knew that General Flynn had misled the Vice President and others", Ms Yates said before the Senate Judiciary subcommittee.

Sally Yates confirmed reports that said had told the White House, six days into Trump's administration, that Flynn, a former military intelligence chief, had not been honest with Vice President Mike Pence about his discussions with the Russian ambassador to Washington.

Yates explained that during her confirmation hearing, future Attorney General Jeff Sessions posed the question to Yates if she would refuse an order "if the President asked me to do something that was unlawful or unconstitutional and one of your colleagues or even that would reflect poorly on the Department of Justice".

Republican senators in the hearing repeatedly pressed Yates on an unrelated matter - her refusal to defend the Trump administration's travel ban - and whether she was responsible for leaking classified information. The trail of Russian collusion, if any, with associates of Donald Trump during the 2016 presidential election has gone stone cold, but the investigation of the suspected Obama administration spying on the Trump team continues to turn up evidence.

At the time, Pence and others had publicly denied that Flynn had discussed easing US sanctions with the Russian official.

Sen. Ted Cruz of Texas, a former Republican presidential candidate, briefly veered away from Flynn, Russia and the Trump administration and into Democratic presidential nominee Hillary Clinton's use of a private email server while secretary of state, an issue that dogged her campaign.

She said Monday she did not - and that she had revealed no classified information herself. Obama had previously warned Trump directly after the election that Flynn was too risky to be trusted, yet Trump appointed Flynn anyway.

Flynn and Kislyak were in touch in late December, including on the 29th, the day the Obama administration levied sanctions in response to a determination by USA intelligence agencies that Russian President Vladimir Putin's government had interfered in the US campaign in an effort aimed in part at helping Trump win.

Yates had initially been scheduled to testify before the House Intelligence Committee last month, but that hearing was canceled by the panel's chairman after a reported legal dispute between Yates' lawyer and the White House about whether she was barred from testifying due to "executive privilege".

Donald Trump sacking FBI's Comey 'reeks of Russian cover up' Democrat claims
That may have been an exaggeration at the time . "That firing led indirectly but certainly to the resignation of President Nixon". But I'll tell you what he did, he brought back his reputation. "Nearly everyone agrees that the director made serious mistakes".

One week before he was sacked, Comey testified before the Senate Judiciary Committee and defended his midnight revelation on the Clinton investigation, although he added, "It makes me mildly nauseous to think we might have had some impact on the election". However, ranking Democrat Sheldon Whitehouse indicated to her that the invitation was made without his agreement, as he believed her presence was not relevant to the topic of the hearing, according to the source.

"They must be congratulating themselves for having exceeded their wildest expectations", he said.

"I hope that current members of Congress recall that it actually doesn't take a lot of courage to aid those who are already powerful, but it does require some courage to champion the vulnerable and the sick", Mr. Obama said. On his show last night, he introduced the topic with his guests by saying, "I wouldn't want to be against her".

Strikingly, Yates warned that not only was Flynn not telling the truth about the calls, the Russians knew and could probably prove he was lying - therefore opening him up to blackmail.

Flynn's forced resignation followed media reports that he had discussed USA -imposed sanctions on Russian Federation with Ambassador Kislyak, which was contrary to the public representations of the Trump White House. The vice president, apparently relying on information from Flynn, initially said the national security adviser had not discussed sanctions with the Russian envoy, though Flynn later conceded the issue may have come up.

Monday's hearing, which is expected to be dominated by Yates' warning to the White House on Flynn, is certain to put him back on center stage in the ongoing Russian Federation investigations.

Yates, a longtime federal prosecutor and Obama administration holdover, had been scheduled to appear weeks ago before the House intelligence committee, but that hearing was canceled.

Asked if Trump's tax returns could be helpful to such an investigation, Graham said: "It could be, down the road".

Hopefully, as the inquiries unfold, more Republicans will follow the example of Senator Ben Sasse of Nebraska, whose thoughtful questions to Clapper and the other witness, former acting attorney general Sally Yates, put his GOP colleagues to shame.