The special counsel appointed to probe alleged Russian meddling in the 2016 United States presidential polls is now also investigating President Donald Trump for possible obstruction of justice, according to a media report.
Now it appears Mueller is examining the president's own conduct, which may include whether Trump tried to obstruct justice.
He also said Comey should have shared his concerns about the Trump conversation with another Justice Department official, Dana Boente, who was then acting deputy attorney general, and would have been Comey's direct supervisor.
Mr Mueller, a widely respected former head of the FBI, has now taken up the angle of possible efforts by Mr Trump to obstruct justice in the investigation, the Post said. House Speaker Paul Ryan and other Republican leaders publicly said they thought the investigation should be allowed to run its course, and that firing the special counsel would be a mistake.
Mueller is seeking to interview Director of National Intelligence Dan Coats and National Security Agency Director Mike Rogers, according to the people, who asked for anonymity because of the sensitivity of the matter.
The move by Robert Mueller to investigate Trump is a major turning point in the hotly contested FBI investigation. The White House initially cited that memo as his reason for the termination, and later said in an NBC interview that he also was influenced by the Russian Federation investigation. However, a finding of wrongdoing would likely be left to Congress to consider whether it warranted criminal impeachment.
The president denies that he asked Comey to drop the Flynn probe, part of his version of the events involving the former director that he said last week he'd be "100 percent" willing to recount under oath.
Ledgett wrote a memo, according to the source, documenting a conversation in which President Donald Trump allegedly urged Rogers to help get the FBI to lift the cloud of the Russian Federation investigation.
There's still an open question as to what, exactly, could happen if Mr Mueller does find the president violated the law in acting to disrupt an ongoing investigation.
Comey said he believed Mueller would look into Trump for obstruction of justice.
"While the president has the right to, he has no intention to do so", Trump spokeswoman Sarah Sanders told reporters. The special counsel also plans to interview Rick Ledgett, who recently retired as the deputy director of the NSA, the person added.
On Tuesday, Attorney General Jeff Sessions told the Senate Intelligence Committee that there were discussions at high levels about firing FBI Director James Comey even before Sessions was confirmed. "I was sacked, in some way, to change - or the endeavor was to change the way the Russian Federation investigation was being conducted". "As long as I'm in this position, he will not be fired if not for good cause", he said.
The Senate committee has already begun taking testimony in both closed and open sessions from the nation's intelligence chiefs.
Trump has said he is "100 per cent" willing to testify under oath on Comey meetings and tell the FBI Special Consul Robert Muller that he never asked FBI to stop investigating. It is unclear if McCabe, Comey's successor, has informed Trump of the change in the scope of the probe.