Mitt Romney, 2012 Republican presidential nominee and Utah Senator-elect, tweeted Wednesday: “I want to thank Jeff Sessions for his service to our country as Attorney General. Under Acting Attorney General Matthew Whitaker, it is imperative that the important work of the Justice Department continues, and that the Mueller investigation proceeds to its conclusion unimpeded.”

Earlier this year CNN asked Romney about the Mueller investigation, and he warned that Congress would need to take action if Trump ever moved toward removing Mueller.

"I do not believe for a moment that President Trump will remove Mueller," Romney said earlier this year. "If he does remove Mueller, I believe that Congress will reappoint him, and the most effective way to keep the investigation intact is for congressional leaders to make it clear to the President that if (Mueller) were removed by the executive branch, he would be rehired by the legislative branch. I presume that communication has happened already."

"I believe it's appropriate for the rule of law to proceed to reach the conclusion of this investigation — hopefully sooner rather than later," Romney said earlier this year when asked whether he still has confidence in Mueller.