Few Cabinet members have had as contentious a relationship with the presidents they serve as did Jeff Sessions, attorney general until approximately 13 hours after the last polls closed in the 2018 midterm elections. Sessions endured President Trump’s frequent critiques on Twitter and was the target of Trump’s frustration both in interviews and in West Wing conversations that were later reported by the media.

The primary reason for Trump’s irritation was Sessions’s decision in March of last year to recuse himself from the Russia investigation. That recusal stemmed from a recommendation by Justice Department attorneys, who noted Sessions’s involvement in Trump’s 2016 campaign posed a potential conflict with an investigation into that campaign. For Trump, though, the recusal was a betrayal that left him exposed. Trump apparently hoped for an attorney general as loyal to his personal interests as Robert Kennedy was (per Trump’s assessment) when he served in his brother’s administration. Sessions should have told him he planned to recuse, Trump said on more than one occasion, and then Trump would not have picked him in the first place.

Sessions’s departure changes that calculus dramatically.

It is unclear how close the investigation into Russian interference in the 2016 election is to being completed, much less the arm of that probe run by special counsel Robert S. Mueller III which is looking at any overlap with Trump’s campaign. There are signs it is nearing completion — but that could mean we are on the brink of substantial revelations or indictments. For example, in recent weeks, Trump’s son Donald Trump Jr. has reportedly told friends he expects to face an indictment. (Experts who spoke with The Washington Post speculated this would explain why Mueller has not yet interviewed Trump Jr.)

In other words, there may still be good reason for Trump to want to curtail Mueller’s work. With Sessions gone, that became much easier in two ways.

The first is installing a new attorney general would mean that control of the Mueller probe shifts away from Deputy Attorney General Rod J. Rosenstein, who appointed Mueller under the authority of leading the probe following Sessions’s recusal. Appointing a new attorney general is not trivial, since that person would need Senate confirmation to start work. Except that, under the terms of the Vacancies Reform Act of 1998, Trump does not need to have a new attorney general go through that process. Because Sessions technically resigned (at Trump’s request), there is no question Trump could use the Act to simply move any other administration official who’s already been confirmed by the Senate into Sessions’s former position. In other words, Trump could in short order name Energy Secretary Rick Perry as attorney general if he wanted to. There are nearly 400 people who have been Senate confirmed, any of whom could presumably be moved over.

He may not need to do that. Trump tweeted news about Sessions’s departure, mentioning the acting attorney general would be Matt Whitaker, previously Sessions’s chief of staff. As our Aaron Blake noted, Whitaker offered his opinion about the Mueller probe shortly before being hired by Sessions: Broadly echoing Trump’s rhetoric about the need to wind down the probe and, perhaps more importantly, defending Trump Jr.'s involvement in a meeting with a Kremlin-linked attorney at Trump Tower in June 2016.

So what could a new Justice Department head hostile to the investigation do? A lot. Earlier this year, we spoke with Louis Seidman, Carmack Waterhouse professor of constitutional law at Georgetown University, who outlined the ways in which Mueller’s wings could be clipped.

The main leverage that person gains:

First and foremost, whoever is the Department of Justice staffer overseeing the probe is granted the power to “request that the Special Counsel provide an explanation for any investigative or prosecutorial step, and may after review conclude that the action is so inappropriate or unwarranted under established Departmental practices that it should not be pursued.” In other words, if Mueller wants to bring forward a new indictment, the person in charge at DOJ could nix it.
They could also go further.
“Depending on how aggressive this person wanted to be, they could dismiss the criminal cases, they could get rid of the grand jury,” Seidman said at the time. “In the end, if Trump is determined, the people he appoints could shut [the probe] down.”

If Mueller wants to indict Trump Jr., he has to ask the Justice Department official overseeing the probe. Rosenstein has already agreed to transfer his oversight to Whitaker, meaning Whitaker is now the one who would answer Mueller’s question.

Marcy Wheeler, a journalist who has been tracking the legal issues involving the Mueller probe, notes that existing, sealed indictments may be out of reach for any Sessions replacement. If an indictment doesn’t exist and if Whitaker is true to what he wrote before joining the government, he could simply respond to Mueller’s request with a “no” — and an indictment would come to a halt.