Michael Flynn has reportedly agreed to testify against Trump and members of his family in the Russia investigation

Former national security adviser Mike Flynn is expected to plead guilty to lying to F.B.I. investigations on Thursday, becoming the fourth individual involved in the Trump campaign to face charges in the ongoing Justice Department investigation into Russia’s interference in the 2016 presidential election, and the second who appears to have cut a deal with special prosecutor Robert Mueller.

The single charge against Flynn, according to a court filing made public Friday, is that he “did willfully and knowingly make materially false, fictitious and fraudulent statements” during a January 24 interview in which he discussed his conversations with Russian Ambassador Sergey Kislyak.

Prosecutors charge that the retired three-star general falsely stated that he did not ask Kislyak to “refrain from escalating the situation” in response the sanctions leveled against Moscow by Barack Obama, or request the ambassador to “delay the vote on or defeat” a pending United Nations resolution over two phone calls in late January. (Flynn came under intense scrutiny for his communications with Kislyak earlier this year, ultimately resigning because of them.)

The fact that Flynn was not charged with any other crimes, as well as the fact that Mueller did not convene a grand jury to secure an indictment, immediately fueled speculation that Trump’s former top adviser is cooperating with the government. For months, a steady drip of news reports have suggested a web of clandestine lobbying efforts by Flynn and his son, Michael G. Flynn, on behalf of foreign governments including Turkey.

Mueller’s apparent hesitance in charging Flynn, despite reports that he already had enough evidence to arrest the pair, was widely interpreted to mean that Flynn’s lawyers were working on a deal. Several days ago, Trump’s lawyers confirmed that the former adviser’s attorney stopped sharing pertinent information tied to the probe with the White House legal team—a move that seemed to confirm that Flynn had, in fact, flipped.

“On its face, it is a really, really good deal for him,” Sol Wisenberg, a white-collar criminal defense attorney who worked on the Whitewater investigation, told me—assuming that Flynn doesn’t face any additional charges and that immunity for his son is part of the agreement. “He is obviously cooperating. There is no way he is not cooperating, there is just no way,” Wisenberg told me. “If he wasn’t cooperating he would be indicted and I guarantee you there would be more counts than this.”

That conclusion appeared to be confirmed later Friday morning by ABC News, which reported that Flynn, facing mounting legal costs and feeling “abandoned” by Trump, had made the decision to cooperate with Mueller. Sources told the outlet that after Flynn was confronted with the full array of potential charges against him, he agreed to testify about President Donald Trump, as well as members of Trump’s family and others in the White House. “He is prepared to testify that president Trump, as a candidate, ordered him and directed him to make contact with the Russians,” ABC’s Brian Rosssaid on air, adding that Flynn was “distraught” about the decision, but “feels he is doing the right thing for his country.”