Jeff Sessions is gone. Here's what that means for Robert Mueller.

This story was last updated at 6:00 p.m. EST

President Trump spent a chunk of time during Wednesday’s post-midterms press conference bemoaning Robert Mueller’s ongoing investigation into his 2016 campaign.

Then he parted ways with one of the key men responsible for it: Attorney General Jeff Sessions.

With the beleaguered AG’s resignation in hand, Trump welcomed a much friendlier face to his ranks: Matt Whitaker, a former U.S. attorney from Iowa who’s been far from shy in his criticism of Mueller’s probe. The hiring of Whitaker spells trouble for special counsel Mueller’s investigation into Trump’s ties to Russia, legal experts told VICE News.

Whitaker, who has accused Mueller of "going too far," is now expected to assume oversight of the the special counsel's investigation from Deputy Attorney General Rod Rosenstein, Bloomberg and NBC reported, citing unnamed sources familiar with the situation. Rosenstein appointed Mueller 18 months ago and has quietly defended the probe from Trump and his allies in Congress ever since.

“The president’s move to demand Sessions resign, and put Whitaker in his place, is obviously part of a strategic effort to limit the Mueller investigation,” said David Kris, who served as assistant attorney general for national security under former President Barack Obama.

Mueller’s new boss at the Department of Justice can dismiss him for “misconduct, dereliction of duty, incapacity, conflict of interest, or for other good cause,” according to the special counsel regulations. But he doesn’t need to fire Mueller to change the shape and scope of the investigation, and Whitaker seems abundantly clear in this regard. “I could see a scenario where Jeff Sessions is replaced,” Whitaker told CNN in July 2017. “It would recess appointment and that attorney general doesn't fire Bob Mueller, but he just reduces his budget to so low that his investigation grinds to almost a halt.”

But Whitaker’s ability to assume full oversight of the Mueller probe may be in question, said Kris, founder of the Culper Partners consulting firm.

Whitaker could potentially be advised to recuse himself by DOJ ethics officials, on the grounds that he was appointed by Trump, who is a subject of the investigation. Whitaker’s appointment could also be legally challenged by outside groups, including newly-empowered Democrats in the House, Kris said.

Mary McCord, the former DOJ official who oversaw the department’s investigation into foreign meddling in the 2016 election before Mueller’s appointment, shared Kris’ skepticism.

“It’s not obvious, from the regulations, that Whitaker will automatically and immediately take over the Mueller investigation,” said McCord. “I think that at a minimum he’d need to do the conflicts of interest check. That’s in the very first line of the special counsel regulations.”

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Barring such a recusal, however, a new Trump-friendly official has considerable power to simply bog down the probe by refusing new investigative steps or blocking prosecutions outright.

“Whitaker could withhold resources, or approval for charging decisions,” said Barbara McQuade, a former U.S. Attorney for the Eastern District of Michigan.

Whitaker’s critical view of Mueller was likely on Trump’s mind when he selected his new acting AG, observers said.

“Mr. Whitaker has been critical of the Mueller investigation, and it’s hard to imagine those critical comments weren’t at least part of the reason why Trump chose him,” said Harry Sandick, a former federal prosecutor turned white-collar defense attorney.

Whitaker has been called the White House’s “eyes and ears” in the Justice Department by Trump’s chief of staff John Kelly, according to an earlier report in The New York Times.

“This is a disturbing development,” said Jens David Ohlin, vice dean of Cornell Law School. “The eyes of history are on Mr. Whitaker and will judge him accordingly, as hero or villain, as the case may be.”

Whitaker’s appointment immediately stirred alarm among Democrats who’ve long sought to protect Mueller through bipartisan means.

Senate Minority Leader Chuck Schumer called on Whitaker to “recuse himself from” the Russia investigation, citing his critical comments of the special counsel. Democratic Sen. Mark Warner, the ranking member on the Senate Select Committee on Intelligence, warned Trump against attempting to obstruct the Mueller probe.

“No one is above the law, and any effort to interfere with the special counsel’s investigation would be a gross abuse of power by the president,” Warner said in a statement to VICE News. “While the President may have the authority to replace the Attorney General, this must not be the first step in an attempt to impede, obstruct or end the Mueller investigation.”

Sessions’ firing is also likely to raise fresh questions surrounding obstruction charges, which already falls under Mueller’s core mandate. Legal analysts said that Trump has the right to fire Sessions, but doing so with the express intent of flummoxing Mueller’s probe could put him in legal jeopardy.

“The president has the right to remove a member of his cabinet,” said Sandick. “But if he takes official action with the clear objective of upending the investigation, then it seems to me that could indeed be construed as the obstruction of justice.”

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Rosenstein has been widely seen as a protective buffer between Trump and Mueller. He has allowed Mueller to expand the probe beyond the narrow question of Trump and Russia, while sticking up for the special counsel’s integrity under withering criticism from skeptical Republican Congressmen.

While the special counsel regulations give Mueller’s boss at the Department of Justice the power to deny specific investigative steps, Rosenstein approved the prosecution of former Trump campaign chairman Paul Manafort, a move that resulted in Manafort’s conviction. Manafort then flipped, and agreed to a sweeping cooperation agreement to tell Mueller everything he knows, including about Trump and Russia.

Despite the looming threat to Mueller, analysts have said Trump will find it difficult to stuff Mueller’s genie back in its bottle.

Mueller has already scored convictions against four Trump aides, turning them into cooperating witnesses. Tangential investigations have been farmed out to other districts, giving them a life of their own far beyond his purview.

Cover image: Then-FBI director Robert Mueller speaks during an interview at FBI headquarters on Wednesday, Aug. 21, 2013, in Washington.