Whitaker was hired as a CNN legal commentator previous year for several months, before leaving the role in September 2017 to head to the Justice Department as chief of staff to now-former Attorney General Jeff Sessions.
That set off immediate alarm bells: Whitaker has been overtly critical of the broad scope granted to Mueller's team to probe beyond allegations Trump's campaign colluded with Russian Federation in 2016, into other ties between Trump, his family and aides, and Russian Federation - an investigation the president calls a "witch hunt". Nobody Is Above The Law said it wants Whitaker to recuse himself from supervising the investigation. "I don't trust him or the people he cloaks himself with", protestor Dawn Roads said.
"Trump has done a naked attempt to mess with the investigation", she said. "Special Counsel Mueller must be allowed to complete his work without interference-regardless of who is AG".
Whitaker is a longtime critic of Mueller's endless Russia probe, which has failed to produce a scintilla of evidence related to Russian collusion. One of those offices, in NY, is leading an investigation involving the president's former personal lawyer, Michael Cohen, and hush money payments Cohen says he made to two women who say they had sex with Trump.
Mueller declined to comment, according to his spokesman, Peter Carr.
Asked if Whitaker would now oversee Mueller, a Justice Department spokeswoman said: "The acting attorney general is in charge of all matters under the purview of the Department of Justice". It has been a privilege to work under his leadership.
Trump asserted that again on Wednesday in a press conference at the White House in which he suggested the only reason he hasn't already ousted Mueller is because it might make him look bad. Trump, who denies any collusion, has long complained about the probe, calling it a witch hunt.
The row, carried live on national TV networks, was followed by Trump issuing angry put-downs to several other reporters.
Despite Trump's criticism of the probe as a "witch-hunt", Sessions and Rosenstein both defended Mueller's integrity.
Now, his chief of staff, Matthew Whitaker, 49, will fill in as Acting Attorney General.
He has said that Hillary Clinton should have been prosecuted for her email scandal as secretary of state and that Trump made the right call in firing FBI Director James Comey.
He also once tweeted a prosecutor's opinion piece that described the Mueller team as a "lynch mob", and wrote his own op-ed saying Mueller would be outside his authority if he investigated Trump's family finances. "There is no mistaking what this means, and what is at stake: this is a constitutionally perilous moment for our country and for the president". The move has sparked concern that Whitaker would end or hamper the investigation. "This is a break-the-glass moment", he said. Chuck Grassley, now chairman of the Senate Judiciary Committee. A permanent replacement will be named at a later point, a second tweet from the president said. And he's one step closer to being able to do just that.
Live, ongoing coverage as nation takes to street to let Trump know that "nobody is above the law".
Those indictments have led to six guilty pleas and three people sentenced to prison.