WASHINGTON — President Trump abruptly announced on Twitter Wednesday that Jeff Sessions is no longer the U.S. attorney general.

“We are pleased to announce that Matthew G. Whitaker, Chief of Staff to Attorney General Jeff Sessions at the Department of Justice, will become our new Acting Attorney General of the United States. He will serve our Country well,” Trump tweeted, adding: “We thank Attorney General Jeff Sessions for his service, and wish him well! A permanent replacement will be nominated at a later date.”

The Department of Justice provided Yahoo News with a copy of an undated resignation letter from Sessions to the president. At the top of the letter, Sessions indicated the president asked him to resign.

“At your request, I am submitting my resignation,” Sessions wrote.

In the past, Sessions has referred to being attorney general as his “dream job.” In the letter, he said he had been “honored to serve.”

The White House did not immediately respond to a request for comment about Sessions’s departure.

Sessions’s exit came within hours of a lengthy White House press conference where Trump suggested some major staff changes would be coming soon.

When pressed, the president declined to say what those changes might be. He framed potential turnover as standard operating procedure after the end of an election cycle.

Jeff Sessions listens as President Trump speaks before he is sworn in as attorney general on Feb. 9, 2017. (Photo: Andrew Harrer/Bloomberg via Getty Images

Trump’s White House has seen extensive turbulence with multiple high-level departures. Sessions has long been seen as having a questionable future with the White House because Trump has repeatedly expressed his disapproval of the attorney general’s decision to recuse himself from special counsel Robert Mueller’s Russia probe.

Sessions’s recusal stems from the fact he was an active supporter of Trump’s 2016 campaign. The Mueller probe is examining whether Trump’s campaign team colluded with Russian efforts to interfere in that presidential race. Sessions’s recusal prevented him from stopping the probe, which Trump has attacked as an unfair “witch hunt.”

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Whitaker, on the other hand, has expressed frustration with Mueller’s probe.

In a CNN op-ed published last year, Whitaker suggested the investigation had gone too far amid reports that the special counsel was looking into the Trump Organization’s financial records.

“Mueller has come up to a red line in the Russia 2016 election-meddling investigation that he is dangerously close to crossing,” Whitaker wrote. “This information is deeply concerning to me. It does not take a lawyer or even a former federal prosecutor like myself to conclude that investigating Donald Trump’s finances or his family’s finances falls completely outside of the realm of his 2016 campaign and allegations that the campaign coordinated with the Russian government or anyone else. That goes beyond the scope of the appointment of the special counsel.”

Matthew Whitaker, left, and Jeff Sessions. (Photos: Charlie Neibergall/AP, Pablo Martinez Monsivais/AP)

On Capitol Hill, reaction to Sessions’s ouster among Democrats was swift.

“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,” Sen. Mark Warner, D-Va., said in a statement. “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.”

“Senators from both parties have repeatedly affirmed their support for Special Counsel Robert Mueller’s investigation,” Warner added. “Every one of them should speak out now and deliver a clear message to the president that the special counsel’s investigation must continue without interference.”

“It is impossible to read Attorney General Sessions’ firing as anything other than another blatant attempt by @realDonaldTrump to undermine & end Special Counsel Mueller’s investigation,” House Minority Leader Nancy Pelosi tweeted. “Given his record of threats to undermine & weaken the Russia investigation, Matthew Whitaker should recuse himself from any involvement in Mueller’s investigation. Congress must take immediate action to protect the rule of law and integrity of the investigation.”

Senate Minority Leader Chuck Schumer agreed.

“Mr. Whitaker should recuse himself from its oversight for the duration of his time as acting attorney general,” Schumer said.

Read Sessions’s letter to Trump below.

This post was updated at 3:37 p.m. with further details including Sessions’ s letter.

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