US President Donald Trump is under investigation for obstruction of justice, the Washington Post reported today.

This is a significant change in the investigation by the FBI, lead by special counselor Robert Mueller, which had previously been looking into possible Russian interference in the 2016 election.

Read More: Why the Probe Into Trump and Russia Is Critical for Global Democracy

President Trump recently fired FBI Director James Comey. Comey testified last week at a Senate hearing that Trump had told him he hoped Comey could stop investigating former National Security Advisor Michael Flynn. Flynn resigned after his various ties to Russia were reported by the media. 

Comey testified that Trump said to him in a private conversation: "I hope you can see your way clear to letting this go, to letting Flynn go... He is a good guy. I hope you can let this go."

The Post reported that Mueller expanded his investigation to include Trump himself after Comey’s testimony.

Read More: Comey: ‘Those Were Lies, Plain and Simple’ 

The Post reported that the FBI is interviewing several senior intelligence officials: Daniel Coats, the current National Intelligence director, Adm. Mike Rogers, head of the the National Security Agency, and Richard Ledget, Rodgers’ recently departed deputy, have all been contacted by the FBI investigation team.

The NSA said it would “fully cooperate with the special council,” the Post reported. 

Obstruction of justice is defined by the United States Constitution as, “whoever . . . . corruptly or by threats or force, or by any threatening letter or communication, influences, obstructs, or impedes, or endeavors to influence, obstruct, or impede, the due administration of justice, shall be (guilty of an offense)."