"So I could see a scenario where Jeff Sessions is replaced ... and that (new) attorney-general doesn't fire Bob Mueller but he just reduces his budget to so low that his investigations grinds to nearly a halt", Mr Whitaker said in a CNN interview in July 2017.
To Trump's unrelenting ire, Sessions was unable to rein in Mueller's expansive probe into Russian interference in the 2016 presidential election and whether the president obstructed justice, given Sessions' decision to recuse himself from the probe in March 2017.
Keep checking the WSAZ App and WSAZ.com for the latest information. Trump, who reportedly referred to Sessions as "Mr. Magoo", did not like the fact that Sessions recused himself from Robert Mueller's Russian Federation probe after consulting with DOJ ethics officials.
"The acting attorney general is in charge of all matters under the purview of the Department of Justice", said department spokeswoman Sarah Isgur Flores.
"I could fire everybody right now, but I don't want to stop it because politically I don't like stopping it", Mr Trump told a White House news conference.
And Sen. Elizabeth Warren tweeted that Trump's firing of Sessions "brings us one step closer to a constitutional crisis", while also calling for Congressional action.
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The senator also tweeted that the president's forceful resignation of Sessions means he "has something to hide".
The top Democrat on the House oversight committee says Congress should investigate "the real reason" for the "termination" of Attorney General Jeff Sessions.
A replacement for Mr Mueller though would have no such constraints, potentially allowing Mr Trump to hamstring the investigators. Today, after a brutal midterm beating and facing the prospect of a dump of damaging indictments from the Mueller camp, the White House has asked for and received a resignation from Jeff Sessions.
"I don't have an attorney general".
A Justice Department official said Whitaker would assume authority over Mueller's investigation. He later lost a Republican primary race against Roy Moore, who went on to be defeated by Democrat Doug Jones.