Whitaker also worked on Sam Clovis's failed campaign for Iowa state treasurer in 2014 after both of them ran unsuccessfully for the U.S. Senate.
The White House said Sessions resigned in a letter to Trump on November 7 and that the president had accepted his resignation as chief of the Justice Department - a move that immediately raised concerns from Democrats, who called for protection for the probe conducted by Special Counsel Robert Mueller.
A Kremlin spokesman, Dmitry Peskov, on Thursday called Mueller's investigation a "headache" for USA authorities but said it "has nothing to do with us", and he declined to comment on Sessions' departure.
A Justice Department spokeswoman, asked if Mr Whitaker would now oversee Mueller, replied: "The acting attorney general is in charge of all matters under the purview of the Department of Justice". However, it would be an immediate priority for Democratic investigations when they officially take control of the House in January.
"Under these conditions, it would be wholly inappropriate for Mr. Whitaker to supervise the Special Counsel investigation given his documented history of opposition to it", Nadler said, before warning that the Sessions firing would be investigated and warning that documents related to the event must be preserved. Trump is also mulling Florida Attorney General Pam Bondi, who is on her way out of office, as well as Trump personal lawyer Rudy Giuliani and former Attorney General William Barr, who served in President George H.W. Bush's administration.
Trump's relationship with Sessions frayed just weeks into his tenure, when he stepped aside from the Russian Federation investigation. "No one is above the law", said Adam Schiff, the top Democrat on the House Intelligence Committee.
That left Rosenstein overseeing the investigation, and he named Mueller as special counsel. Kobach, who has built a national profile as an advocate of tough immigration laws, advised Trump's campaign and the White House on homeland security issues and has made enacting state policies against illegal immigration a cornerstone of his campaign for governor.
She went on to argue that, "given his record of threats to undermine and weaken the Russian Federation investigation", Mr Whitaker should follow in Mr Sessions' footsteps and recuse himself.
The department's numer two, Deputy Attorney General Rod Rosenstein, took over and appointed Mr Mueller after Mr Trump fired then-FBI Director James Comey in May 2017. And he's one step closer to being able to do just that.
"Trump putting himself above the law is a threat to our democracy, and we've got to get Congress to stop him", the group said on its website.
After recusing himself from the Russian Federation probe, the staunchly conservative Sessions spent his time ramping up efforts to combat violent gangs, drug use and illegal immigration - all key components of Trump's law-and-order agenda.
-With assistance from Steven T. Dennis.