Washington (CNN) Jeff Sessions ' ouster as attorney general was a long time in the making, but his sudden departure Wednesday has sent Washington scrambling over what it means for special counsel Robert Mueller's investigation as it nears its expected conclusion.

President Donald Trump appointed Sessions' chief of staff Matt Whitaker, an outspoken skeptic of the Russia investigation, to acting attorney general. In that position Whitaker is expected to take the reins from Rod Rosenstein, deputy attorney general, and oversee Mueller's inquiry.

As acting attorney general, Whitaker will have say over key decisions, such as whether to subpoena the President, approve criminal charges of individuals and directions over the scope of the investigation as more information comes to light.

Whitaker will also decide if the final report prepared by Mueller should be made public as well as which portions to redact.

Many Democrats are calling for him to recuse himself since he has previously suggested limits to the inquiry.

"I'm very concerned," Preet Bharara, a former US attorney for the Southern District of New York during the Obama administration, said on CNN. It "looks like you have someone who has prejudged the Mueller investigation ... there might be an undue restricting of the investigation."

Given Trump's frustration with Sessions for having recused himself from the Russia probe, a move that put Rosenstein in charge of it, Bharara added, "You've got to believe the President got a different kind of understanding" from Whitaker.

Early reactions from the White House were to downplay an abrupt ending of the special counsel's investigation.

Rudy Giuliani, one of Trump's attorneys, said of the inquiry. "It's gone on this long, I can't imagine he would end it now." Giuliani is one of the attorneys helping prepare the President's written answers to questions from Mueller's team.

Limits on Mueller's investigation would not mean all criminal inquiries would end.

Mueller's team, including attorneys hired for the investigation as well as career FBI agents, have been working diligently behind the scenes. It's likely active criminal investigations would continue in another format even if the special counsel inquiry were shut down.

Officials could make referrals of ongoing investigations to other US attorney's offices. There could also be sealed complaints or indictments of numerous individuals that Mueller's team could rush to make public.

Called for limits on Mueller

But others were speculating that Whitaker, a former US attorney who has also dabbled in politics, would could impact the probe less directly by limiting its funding or scope based on his prior statements. Whitaker was the campaign chairman for Sam Clovis in 2014 when Clovis ran for state treasurer in Iowa, according to an archived press release on Clovis' website. Clovis, who was a member of Trump's campaign, was interviewed as part of Mueller's inquiry.

Whitaker wrote in an op-ed on CNN.com last August before joining the Justice Department, that any inquiry that touched the President's finances would be off-limits. "It is time for Rosenstein, who is the acting attorney general for the purposes of this investigation, to order Mueller to limit the scope of his investigation to the four corners of the order appointing him special counsel.

"If he doesn't, then Mueller's investigation will eventually start to look like a political fishing expedition," he added.

Whitaker told Don Lemon on CNN Tonight in July 2017 that a new attorney general wouldn't need to fire Mueller to revamp the inquiry but could take steps that "reduces his budget so low that his investigation grinds to almost a halt."

"So, I could see a scenario where Jeff Sessions is replaced with a recess appointment," Whitaker said, "and that attorney general doesn't fire Bob Mueller, but he just reduces his budget to so low that his investigation grinds to almost a halt."

Democratic lawmakers said Sessions' forced resignation was an attempt by Trump to take control of the investigation with some going so far as to suggest any changes would amount to obstruction.

House Minority Leader Nancy Pelosi called Sessions' firing "a blatant attempt" by the President to undermine the Mueller inquiry. She also called for Whitaker to recuse himself "given his record of threats to undermine and weaken the Russia investigation."

Whitaker has already publicly said one area Mueller's team is scrutinizing is not illegal -- Trump's firing of FBI Director James Comey.

"There is no criminal obstruction of justice charge to be had here," Whitaker said in a radio interview in June 2017. In the interview, which followed Comey's congressional testimony about his encounters with Trump, Whitaker said, "There's no criminal case that could be substantiated on these facts no matter how good of a witness Jim Comey appears to be, and he was very impressive yesterday."

Democrats, who are poised to take control of the House, have indicated they will keep pressure on the Justice Department and are preparing in any event for a shutdown of the inquiry.

New York Democratic Rep. Jerry Nadler, who is expected to become the chairman of the House Judiciary Committee in January, said he is "immediately issuing multiple letters to key officials demanding that they preserve all relevant documents related to this action to make sure that the investigation and any evidence remains safe from improper interference or destruction."