While most Republicans remained silent about the firing of Mr Sessions - among them SC senator Lindsey Graham, who said past year there would be "hell to pay" if the attorney general was got rid off - three senior members of the party urged Mr Trump to allow Mr Mueller complete his probe.
Susan Collins, the Republican senator from ME, and one of the party's more moderate elected politicians, also praised Mr Sessions, saying he was "a leader of integrity who served our country well".
Matt Whitaker has been named acting USA attorney general following the resignation of Attorney General Jeff Sessions. He had frequently publicly castigated Sessions for recusing himself previous year from the case. He was ostensibly fired the day after the midterm elections by President Trump. "The president could, and has in our nation's history, said stop investigating this person or please investigate this other person".
Laurence Tribe, a constitutional law professor at Harvard University, said Trump's replacement of Sessions with Whitaker was arguably an impeachable offense in itself.
Whitaker is legally allowed to serve as acting attorney general for no more than 210 days under the Vacancies Reform Act but could be in the post longer while another individual's nomination is pending, according to the Times.
As Sessions' deputy, Rod Rosenstein has been the authority over Mueller's probe, but multiple media outlets are reporting that he has officially been removed from oversight of the investigation. Last year Sessions recused himself from overseeing the Mueller probe, which has been a constant source of anger from the president. Sessions had endured months of public abuse from Trump, who soured on Sessions because he recused himself from oversight of the Russian Federation investigation shortly after he arrived at the Justice Department. Whitaker wrote. "If he doesn't, then Mueller's investigation will eventually start to look like a political fishing expedition".
The announcement, which came in a tweet, comes after months of speculation that Sessions could be on his way out after recusing himself from the investigation into Russian interference in the 2016 presidential elections. The move has sparked concern that Whitaker would end or hamper the investigation.
In piercing attacks, Trump called Sessions weak and beleaguered, complained that he wasn't more aggressively pursuing allegations of corruption against Democratic rival Hillary Clinton and called it "disgraceful" that Sessions wasn't more serious in scrutinizing the origins of the Russian Federation investigation for possible law enforcement bias - even though the attorney general did ask the Justice Department's inspector general to examine those claims.
The White House is bracing for the probe of Donald Trump's presidential campaign to fire up again.
That left Rosenstein overseeing the investigation, and he named Mueller as special counsel.