The former U.S. attorney for the Southern District of New York, Preet Bharara, on Monday disputed a claim by a lawyer for President Donald Trump that the President “cannot obstruct justice because he is the chief law enforcement officer.”

“I have a lot of experience with John Dowd,” Bharara said in an interview with NPR’s Steve Inskeep, referring to Trump’s lawyer. “He represented some high profile people in cases before my office. And he said then, as he’s saying now, a lot of incorrect, mistaken and, on occasion, ludicrous things, so I don’t put a lot of stock in it.”

“The mere fact that the President is the President doesn’t immunize him from an accusation of obstruction,” Bharara added.

Trump fired Bharara in March after he refused to step down at the President’s request. Trump had originally promised Bharara that he would keep his job as U.S. attorney.

Dowd on Sunday claimed responsibility for drafting a tweet sent from Trump’s Twitter account in which Trump claimed to have fired former National Security Adviser Michael Flynn “because he lied to the Vice President and the FBI.”

The President hadn’t previously claimed to know that Flynn had lied to the FBI prior to his firing. Bharara explained the significance of the tweet.

“It matters because it’s a change from what the reasoning was that was given by the President in the first place,” he said. “A few days after [Flynn] became the national security adviser, the President said only that he’d fired Michael Flynn because he had lied to the vice president.”

“And now you have the interjection of a new reason, apparently, which was that he knew, the President knew, that there was a lie to the FBI, which then suggests, that if he did that and knew that before he asked Jim Comey, the FBI director, to back off the investigation— That shows a level of knowledge and intent that was previously unknown,” he said.

Obstruction of justice, Bharara added, is “clearly one of the things that’s being looked at by special counsel Mueller and his team.”