Deputy attorney general Rod Rosenstein submitted a widely circulated memo to the president last month raising concerns over Mr Comey's performance, but Mr Trump later said he had already made the decision to fire Mr Comey.
The Democratic National Committee, in a statement Friday, said that Rosenstein, who has authority over Mueller, needs to recuse himself from the Russian Federation investigation and that control of the investigation should not be given to another presidential appointee.
The Washington Post reported on Wednesday that investigators were looking into possible obstruction of justice.
The President's words of apparent confirmation come after a week of reports from Washington that his firing of Mr Comey, who was heading up a probe into his former National Security Adviser Michael Flynn and his possible ties to the Kremlin, had led the investigation to broaden its scope.
"After 7 months of investigations & committee hearings about my "collusion with the Russians, nobody has been able to show any proof".
Man dies in Niagara Falls after surviving 2003 plunge
Wallenda said she hoped her performance would inspire others - and she offered a special message for other females. In February, an eight-person pyramid, featuring Nik Wallenda , atop a high wire collapsed.
In recent weeks, there has been a lot of reporting that Trump has grown frustrated that there is a "Russia cloud" hovering over his presidency and wants to find a way to remove it.
But at the White House today, spokeswoman Sarah Huckabee Sanders acknowledged to reporters that Mueller had been at the White House - just the day before he was appointed as Special Counsel. Terming Comey's allegations untrue, Trump later said he was willing to testify under oath but Mueller's reported investigation into the president's actions means that Trump will have to live with the ghost of another probe reaching to the White House.
There's no guarantee that the office of the special counsel will pursue this line of investigation, says Entous - these meetings are merely the first step to help investigators determine whether there's more evidence to uncover about obstruction of justice.
Given that every morning brings with it some new Trump scandal, one could be excused for not realizing that Trump has yet to be actively investigated.
Trump's friend Newt Gingrich - who is out with a new book titled "Understanding Trump" - is among those raising questions about the "anti-Trump" focus of Mueller's investigation.
Trump previously suggested that the Flynn investigation be dropped, Comey alleged.