Whitaker had served as Sessions' chief of staff.
Sessions recused himself from managing the investigation because of his own past involvement in the Trump campaign.
In the letter, the group of state attorneys general note that Rosenstein appears to have adequately overseen the Russian Federation probe and "should continue to do so, as Mr. Mueller's work must proceed free from interference or supervision that would appear to many Americans to be biased".
But it's not typical for chiefs of staff to replace the head of an agency when that head resigns, as former CIA staffer and NBC contributor Ned Price pointed out.
The next month, Whitaker wrote an op-ed posted on CNN's website in which he argued that Mueller's investigation appeared to be going too far and may constitute a "witch hunt", echoing one of Trump's favorite descriptions to criticize and discredit the probe. "That's why Cabinet Secretaries have Deputies".
Both Whitaker and Clovis are rooted in Iowa politics, and both ran for the 2014 Republican Senate nomination.
Critics worry Whitaker may be unlikely or unwilling to defend the investigation, given his history of partisanship and loyalty to Trump.
"I used to live in NY and know lots about Trump".
Trump had repeatedly been talked out of firing Sessions until after the midterms, but he told confidants in recent weeks that he wanted Sessions out as soon as possible after the elections, according to a Republican close to the White House who was not authorized to publicly discuss private conversations.
"[Whitaker] is a strong supporter of President Trump's agenda on religious liberty, immigration, drugs, violent crime, and protecting the rule of law", a senior Trump administration official who was not authorized to speak on the record tells Conservative Review.
Since stepping into his new role on Wednesday, Whitaker has faced questions - principally from Democrats - about whether he should recuse from the Russian Federation investigation, given that he has written opinion pieces in the past about the investigation, and is a friend and political ally of a witness.
"The video is clear, he did", she said.
Rep. Jerry Nadler demanded an explanation immediately after the announcement.
Sessions had been protected for much of his tenure by the support of Senate Republicans, including Judiciary Committee Chairman Chuck Grassley, who had said he would not schedule a confirmation hearing for another attorney general if Trump fired him.
"This president's Department of Justice has done a fine job breaking the back of the opioid crisis...prosecuting some doctors, pharmacists and nurses...shutting down the dark web...certainly putting it to the MS-13 gangs and prosecuting many violent criminals, trans-national criminals", she stated. "A permanent replacement will be nominated at a later date". "I could fire everybody right now, but I don't want to stop it because politically I don't like stopping it", Trump said at a stormy White House press conference that was even more tempestuous than the standard he has set.
How many people will show up remains to be seen.