President Donald Trump’s plea that former FBI Director James Comey drop his investigation into former National Security Adviser Michael Flynn is “evidence” that Trump tried to obstruct justice, according to Comey.

Comey made his claim in a much-hyped interview with ABC that aired Sunday night.

Special counsel Robert Mueller is investigating whether Trump tried to obstruct justice as part of his intensifying Russia probe, and the exchange with Comey could be a key part of his case.

The conversation between Trump and Comey took place during a February 2017 Oval Office meeting, first reported by the New York Times in May 2017. During the meeting, Trump asked Comey to “let this go,” referring to the investigation into Flynn. The report was based on notes that Comey kept about his tenure at the FBI after Trump had taken office.

Trump fired Flynn from his post at the White House in February 2017 for allegedly lying to Vice President Mike Pence about the contents of phone calls Flynn made in December 2016 to Russian Ambassador Sergey Kislyak. Flynn discussed US sanctions against Russia with Kislyak and then lied to federal investigators about the contents of the call.

During Sunday’s interview, Comey said he took Trump’s comment about letting Flynn go as a “direction.” “It’s certainly some evidence of obstruction of justice,” Comey told ABC’s George Stephanopoulos.

Comey went on to say the judgment as to whether Trump was trying to interfere with the investigation would come down to “his intent.”

Trump has denied telling Comey to back off the investigation, while his son Donald Trump Jr. went on television to argue that the president’s words weren’t meant as an order but instead as a “Hey, hope this happens” statement.

What Trump knew about Flynn

One of the big questions is whether Trump knew Flynn had lied to investigators when he allegedly asked Comey to drop the case.

Trump tweeted in December that he “had to fire” Flynn because he’d lied to the FBI, seemingly confirming that he knew Flynn had committed a crime when he got rid of him. Trump’s lawyer John Dowd, who recently left the president’s legal team, later claimed he’d written the tweet and that it was incorrect.

Comey’s account has remained consistent in describing Trump’s push to get the Flynn investigation dropped. In addition to his memos, Comey repeated the claim in June when he testified before Congress.

But as Comey noted Sunday, the big question that remains is whether Trump intended to try to interfere with an investigation. Comey said there’s “evidence,” but he has not concluded that Trump definitely did obstruct justice. That would be one reason that investigators want to question Trump directly as part of Mueller’s Russia probe.