U.S. Attorney General Jeff Sessions has resigned at the request of President Trump.
It's unclear what Sessions's departure will mean for the ongoing election interference probe, led by special counsel Robert Mueller.
On Capitol Hill, Senate Minority Leader Chuck Schumer (D-N.Y.) said "Protecting Mueller and his investigation is paramount".
Whitaker, U.S. Attorney for the Southern District of Iowa during the George W. Bush administration, vied for the GOP Senate nomination in Iowa in 2014 but lost to Sen.
Sessions should earn praise for honestly running his department in a fashion no Obama attorney general ever did: he didn't act as Trump's wingman, but as the chief law enforcement officer of the United States.
"While the constitution grants the president the authority to dismiss his cabinet members, we will be keeping a close watch on the future of the special counsel's investigation and the impact of the appointment of a new Attorney General".
Mr Rosenstein in turn appointed Mr Mueller, a former Director of the Federal Bureau of Investigation. Trump tweeted Monday that "investigations of two very popular Republican Congressmen were brought to a well publicized charge, just ahead of the Mid-Terms, by the Jeff Sessions Justice Department".
Trump also tweeted an attack on the Robert Mueller's probe into the Russian collusion, quoting an NBC News survey on publication perception of the probe.
In August of 2017, Whitaker wrote an opinion piece for CNN that was critical of the Mueller investigation.
Whitaker also said legislation to protect Mueller would be "a mistake" in a tweet previous year, adding that the nation "cannot have anyone unaccountable in executive branch".
But everything changed when he recused himself from the Russia investigation after it transpired that he had failed to disclose meetings with Russian officials. As one might expect in this overlapping morass, Trump's going with "the interpretation that lets him do whatever he wants".
Democratic Rep. Adam Schiff of California, who is expected to take over the gavel on the House Intelligence Committee, vowed that Democrats will "protect the rule of law".
"I could see a scenario where Jeff Sessions is replaced", 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 nearly a halt".
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