President Donald Trump called his former personal lawyer Michael Cohen a liar and “weak” after he pleaded guilty Thursday to a new federal charge and agreed to cooperate with Special Counsel Robert Mueller’s investigation of the president’s campaign.

“This is a weak person and not a very smart person,” Trump told reporters Thursday as he departed the White House on his way to the Group of 20 summit of global leaders in Argentina. Cohen is trying to reduce his prison sentence “by making up a story,” the president continued. “Michael Cohen is lying.”

In a New York courtroom earlier in the morning, Cohen admitted to lying in 2017 to the House and Senate Intelligence Committees about Trump’s plans for a Moscow real estate project. Cohen said he told lawmakers that efforts to develop a Trump tower ended in January 2016, “when in fact they continued until June 2016,” deeper into Trump’s presidential campaign.

Trump said at the White House that he had decided not to pursue the Moscow project, but that there would have been nothing wrong if he had. He said he had been focused on running for president in 2016 but that no rule prevented him from continuing to do business.

The new charge is notable because it was brought by investigators on Mueller’s team, who are looking into possible collusion between the Trump campaign and Russians in the 2016 election. Mueller had previously referred Cohen matters to federal prosecutors in New York, where he pleaded guilty to campaign finance and tax violations earlier this year, and has cooperated with Mueller without a formal cooperation agreement. He’s spent dozens of hours providing testimony, a person familiar with the matter has said.

Senator Mark Warner, the top Democrat on the Senate Intelligence Committee, told reporters, “If anything the president is said is true — that there’s no there there — why are all of his closest associates being found guilty of lying about their ties to Russia?”

Cohen’s new guilty plea concerns a statement he submitted to the intelligence panels in August 2017 in which he said talks about the potential Trump tower ended “before the Iowa caucus and months before the very first primary.” In fact, Trump had secured the Republican presidential nomination by the time the talks ended.

Trump has repeatedly criticized the Mueller probe as unfair and denied any collusion between Russia and his campaign. Earlier Thursday, he attacked the probe in a tweet as an “illegal Joseph McCarthy style Witch Hunt, one that has shattered so many innocent lives.”

The president said Wednesday that he hasn’t ruled out pardoning his former campaign chairman, Paul Manafort, after the convicted felon’s plea agreement with Mueller fell apart this week.

Warner said Thursday that Congress would have to act if the president moved to pardon anyone Mueller has been investigating. “”That would be a complete abuse of power,” he said. “The power to pardon has not ever been used to protect a president and his family.”