Former acting Attorney General Sally Yates, who was fired by President Donald Trump after she refused to enforce his controversial immigration executive order, will give testimony to a Senate Judiciary subcommittee on Monday about Russia’s interference in the 2016 presidential election.

Yates is expected to detail conversations she had with the White House to warn the administration of former national security advisor Michael Flynn’s dubious affiliation with Russian ambassador Sergey Kislyak.

Flynn was forced to resign after it emerged he had misled Vice President Mike Pence, as well as other members of the Trump administration, over calls he’d had with Kislyak in December 2016. During those phone calls, Flynn allegedly gave guarantees that the then-incoming administration would lift U.S. sanctions on Russia.

Yates claims to have told White House Counsel Don McGahn in January that she had “serious concerns” about Flynn, who was later dismissed in mid-February after the nature of those concerns went public. Both White House chief of staff Reince Priebus and press secretary Sean Spicer both claimed at the time that Yates’ information on Flynn had amounted to nothing.

The president tweeted a deflection of accountability this morning.

General Flynn was given the highest security clearance by the Obama Administration – but the Fake News seldom likes talking about that. — Donald J. Trump (@realDonaldTrump) May 8, 2017

In 2012, former President Barack Obama had nominated Flynn as director of the Defense Intelligence Agency. He then resigned from the military in 2014, over his chaotic and aggressive managerial style. The Trump administration, however, would have been required to vet Flynn independently for his position as national security advisor.

Trump promptly followed that tweet with another, hinting that Yates may have illegally dropped classified information to the media.

Ask Sally Yates, under oath, if she knows how classified information got into the newspapers soon after she explained it to W.H. Counsel. — Donald J. Trump (@realDonaldTrump) May 8, 2017

Yates has also been invited to finally testify before the House Intelligence Committee—which is also digging into Russia’s involvement in the election—more than a month after committee’s then-chairman Rep. Devin Nunes (R-Calif.) canceled the hearing. Nunes, who was on Trump’s transition team, has since stepped aside after questions arose as to his ability to fairly lead the investigation.

The White House itself was reported to have been involved in the attempt to block Yates’ testimony, when the Justice Department issued letters citing Yates’ Flynn warnings with the administration could be protected by “presidential communications privilege” and therefore unusable—which raised further anticipation as to what it may reveal.

The hearing is set to begin at 1.30pm CT and can be watched via live stream here.