Whitaker himself meanwhile offered little clue about his intentions in a bland statement to reporters thanking Trump for his appointment, praising his former boss as a "dedicated public servant" and adding he would work to leading a department that conformed to the "highest ethical standards".
Trump has not said whom he will nominate to permanently replace Sessions.
The Appointments Clause of the U.S. Constitution states that some senior government officials, known as "principal officers", must be confirmed by the Senate. I did not know Mr. Whitaker. After Sessions' firing, Trump quickly appointed Matt Whitaker as acting attorney general. Another protester showed up in a full inflatable body suit depicting President Trump as a baby, bottle in hand.
Because Sessions had recused himself, Deputy Attorney General Rod Rosenstein supervised Mueller's investigation.
On Friday morning, the Washington Post published a story headlined "Acting attorney general Whitaker has no intention of recusing himself from Russian Federation probe, associates say", and included in the lead paragraph that "people close to him ... do not believe he would approve any subpoena of President Trump as part of that investigation".
Whitaker was tapped by the White House to serve as Sessions' chief of staff in September 2017, with sources describing then-White House counsel Don McGahn as the person behind the hiring. "With the essential firing yesterday of Attorney General Jeff Sessions, we now have acting Attorney General Matthew Whitaker who has already demonstrated his opposition to the Mueller investigation".
Legal scholars, meanwhile, have debated the constitutionality of Whitaker's appointment, with some lawyers saying it is illegal because Whitaker has not been confirmed by the Senate.
Once a US attorney for the Southern District of Iowa, Whitaker also served as a legal commentator at CNN until he joined the DOJ in September 2017. "He was always extremely highly thought of, and he still is".
He also called Whitaker "a very highly respected man".More news: Juventus vs. Manchester United live stream
The White House doesn't release lists of visitors.
"I study political science at the university, and one of the things that motivates me as a political scientist is the fact that I see the norms of our democracy disappearing as Trump continues doing what he does", Tabani said.
By Wednesday afternoon, there were multiple, nationwide calls for rallies in support of Mueller as fear grew over Whitaker potentially ending the investigation. Look for Whitaker to reduce Mueller's operating budget, pull lawyers and investigators now working on Mueller's team back to DOJ, refuse to authorize grand jury subpoenas or indictments, and/or push Mueller to wrap up the probe as soon as possible.
The Senate's top Republican predicted a permanent replacement could be named soon for Mr Whitaker, who is now overseeing the Trump-Russia probe.
Now Whitaker, 49, leads everything at the Justice Department - including the Russian Federation probe. "We're protesting Trump installing a hack to obstruct Mueller's investigation".
He said he was speaking only for himself and he hoped Republicans might join as plaintiffs if a lawsuit goes forward.
Democrats winning back the House isn't entirely bad for Trump.
In that scenario, Mueller's budget could be reduced "so low that his investigation grinds to nearly a halt", Whitaker said during an interview with CNN in July 2017 before he joined the Justice Department.