President Donald Trump’s former attorney Michael Cohen has reached an apparent cooperation agreement with Robert Mueller’s special counsel, pleading guilty to lying to Congress about the extent and nature of his work on a Moscow real estate deal during the 2016 election.

Cohen had told Congress in closed-door testimony to the Senate Intelligence Committee that the Trump Tower deal in Moscow had been halted in January 2016, when he had worked on the project at least through June of that year. The deal has been a focus of Mueller’s investigation, as the special counsel probes connections between Trump associates and Russians. According to ABC News, Trump, who just this week submitted written responses to questions from Mueller, had been asked about the Trump Tower Moscow project in those questions.

Cohen had minimized in his testimony the amount of contact he had with Russian officials over the project and otherwise lied about the discussions surrounding the deal, which never was finalized. Cohen’s guilty plea Thursday is the first instance in which Mueller’s office has charged Cohen. He had previously pleaded guilty to campaign finance charges stemming from an investigation by the office of the Southern District of New York .

Trump’s former lawyer, who was known to be voluntarily cooperating with the special counsel investigation since pleading guilty to those campaign finance charges in August, gave 70 hours of interviews to the investigation, according to ABC News. The questioning focused on contacts between Trump associates and Russians, Trump’s business ties to Russia, obstruction of justice, and talks of pardons. The implications of this testimony are not yet known, but it has the potential to be explosive and highly damaging to the president. “Michael Cohen is lying and he’s trying to get a reduced sentence for things that have nothing to do with me,” Trump told reporters on the White House lawn.

Cohen’s plea deal in August with federal prosecutors in the Southern District of New York directly implicated Trump , and Cohen has maintained that he arranged hush-money payments to kill the stories of women who alleged to have had affairs with Trump “in coordination with, and at the direction of” the president. He is scheduled to be sentenced on the campaign finance–related charges in two weeks. According to reports from the courtroom Thursday, the judge has ordered an expedited sentencing report in an effort to combine the sentencing for the new guilty plea with Cohen’s other case.

The president has grown increasingly vociferous in his attacks on the special counsel investigation, repeatedly asserting on Twitter that it amounted to a “witch hunt” and “McCarthyism.” He also accused Mueller of “viciously telling witnesses to lie about facts.” This week, Mueller also accused Paul Manafort, Trump’s former campaign manager, of lying to investigators in violation of his plea deal agreement. That agreement has since been ended and it has been revealed that Manafort continued to feed information to Trump’s legal team after agreeing to work with Mueller. A key court date in Manafort’s sentencing comes on Friday.