Democratic Representative Jerrold Nadler, who is in line to become chairman of the House Judiciary Committee in January, said it is "wholly inappropriate" for Whitaker to take over the Mueller probe and that Rosenstein should continue overseeing it.
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". He said there was no evidence of collusion. Conway says that Rosenstein was at the White House Thursday and Friday. Despite their House victory, Democrats still appear divided and Trump seems intent on driving a wedge in their ranks, repeatedly expressing his support for veteran Nancy Pelosi, 78, as the Speaker, even though the younger and more radical wing of the party want a younger, fresher face.
Instead, the congressman said, the fact Sessions "followed the rules and simply was not involved at all in overseeing the Mueller probe was grounds for this rather long-awaited firing, and all of the public berating that went along with it".
"Clearly, the President has something to hide", Schumer wrote on Twitter on Wednesday, later adding: "Mr Whitaker should recuse himself from (the probe's) oversight for the duration of his time as acting attorney general".
He also said on CNN previous year that he could see a scenario in which Sessions' replacement doesn't fire Mueller but "just reduces his budget to so low that his investigation grinds to nearly a halt".
On Wednesday, Goodlatte issued a statement praising Sessions' service as attorney general and wishing Whitaker well in his new role. He wrote a year ago on CNN.com that Deputy Attorney General Rod Rosenstein should limit the scope of Mueller's investigation to stop him from delving into Trump's finances.
"It's unfortunate that we all knew the president was going to try to get rid of Jeff Sessions", Warner, a Virginia Democrat, said.
Whitaker has made it known that he is hostile to the probe into whether the Trump campaign colluded with the Russians and the president obstructed justice.
It is not clear how long Whitaker will be the acting attorney general, as a discussion about a permanent replacement is underway at the White House in the wake of Sessions' resignation.
Jerry Role, a retired Department of Justice staffer told Al Jazeera that Trump's actions this week threatened the integrity of U.S. democracy.
In July 2017, he said during an interview on CNN that he could envision a scenario under which a temporary attorney general doesn't fire Mueller but rather "just reduces his budget to so low that his investigations grinds to nearly a halt".
According to USA media reports on Thursday, Mueller's team have started writing the final report of the investigation.
Over the course of his investigation thus far, Mueller and his team of prosecutors indicted 32 individuals and three Russian businesses on charges ranging from computer hacking to conspiracy and financial crimes.