Sally Yates. Pete Marovich/Getty Images) Former Deputy Attorney General Sally Yates will testify at a Senate judiciary subcommittee hearing that she warned the White House in January that former national security adviser Michael Flynn could be susceptible to Russian blackmail, according to CNN.

Such testimony would amount to a forceful public rebuke of President Donald Trump's claim that he was not aware that Flynn had discussed the issue of US sanctions on Russia with Sergey Kislyak, Russia's ambassador to the US, during the transition.

Yates, then the acting attorney general, reportedly traveled to the White House in late January to warn administration officials that Flynn had been misleading Vice President Mike Pence about his conversations with Kislyak, which she said made him vulnerable to being blackmailed by Russia.

Then the vice president-elect, Pence had insisted in an earlier interview with CBS that Flynn and Kislyak "did not discuss anything having to do with the United States' decision to expel diplomats or impose censure against Russia" — a statement that turned out to be untrue and set off alarm bells at the Justice Department.

Yates reportedly told White House Counsel Don McGahn that she had "serious concerns" about Flynn. But he was not asked to resign until February 13, at least two weeks after Yates visited the White House.

Trump, moreover, continued to deny that he knew about what Flynn discussed with Kislyak as late as February 10, when he said he was not aware of reports that Flynn had discussed the issue of sanctions with Kislyak in phone calls and text messages and that he would "look into it." One of his advisers, White House counsel Kellyanne Conway, said in an interview hours before Flynn resigned that he still "had the full confidence of the president."

White House press secretary Sean Spicer told reporters one day later that Yates had gone to the White House to give them "a 'heads up' to us on some comments that may have seemed in conflict with what he (Flynn) had sent the Vice President."

Yates was fired as acting attorney general after refusing to enforce Trump's first executive order on immigration in late January. Interest in her testimony grew even more last month after The Washington Post reported that the White House had tried to prevent her from testifying publicly before the congressional intelligence committees. The White House has denied the charge.

Yates will testify before the Senate Judiciary subcommittee next Monday, May 8. She has also been invited to testify before the House Intelligence Committee, which had planned to interview her publicly alongside former CIA Director John Brennan and former Director of National Intelligence James Clapper in late March. That hearing was scrapped by the House Intelligence Committee Chair Devin Nunes, who has since stepped aside from the probe.