Former acting Attorney General Sally Yates will testify before a congressional committee Monday about contacts between Trump aides and senior officials in the Russian government.

The focus of the hearing will concern former National Security Advisor Lt. Gen. Michael Flynn, who resigned in disgrace after misrepresenting the nature of his communications with Russian Ambassador Sergey Kislyak to Vice President Mike Pence. Yates’ testimony will affect the trajectory of a scandal that has hounded the Trump administration from its first days in office.

Anonymous sources inside the intelligence community accused Flynn of offering to relax U.S. sanctions against Russia during a conversation with Kislyak in late December 2016. If true, such actions could violate the Logan Act, which precludes private citizens from negotiating with foreign governments. No person has ever been prosecuted for a Logan Act violation.

Pence and other administration officials denied the allegations, but Flynn resigned after press reports indicated U.S. spy agencies had a transcript of the conversation.

Yates met with White House Counsel Don McGahn Jan. 26 to discuss Flynn’s account of his contacts with Kislyak. Some reports indicate Yates told the White House that Flynn’s explanations were inaccurate, leaving him open to blackmail or manipulation by Russian officials.

The hearing Monday before the Senate Committee on the Judiciary will mark the first time that Yates has given a public account of her Jan. 26 conversation with the White House Counsel and other senior administration officials, including FBI Director James Comey. Her testimony could contradict previous statements made by the White House about her meeting with McGahn, which Trump aides have repeatedly characterized as little more than a “heads up.”

Should Yates’ testimony controvert the administration’s version of events, new questions could emerge as to the integrity of the White House’s public statements with respect to Flynn’s resignation and the actions of top Trump aides following the Jan. 26 meeting.

Former Director of National Intelligence James Clapper will also appear before the committee. Yates was dismissed Jan. 31 after she announced the Justice Department would not defend President Donald Trump’s first executive order on immigration from seven countries that act as terrorist havens and a moratorium on refugees.

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