US Attorney General Jeff Sessions speaks during an event at the Justice Department May 12 in Washington, DC. Sessions was presented with an award "honoring his support of law enforcement" by the Sergeants Benevolent Association of New York City during the event.
US Attorney General Jeff Sessions speaks during an event at the Justice Department May 12 in Washington, DC. Sessions was presented with an award "honoring his support of law enforcement" by the Sergeants Benevolent Association of New York City during the event.
PHOTO: Win McNamee/Getty Images
Now playing
02:18
Sessions, from Eagle Scout to former attorney general
Now playing
03:19
Some GOP lawmakers are defying Capitol security measures
PHOTO: CNN
Now playing
01:17
Sen. Romney: Senate trial after Trump leaving office is constitutional
PHOTO: CNN
Now playing
03:25
Biden's HHS secretary pick: If we do this, we will get the pandemic under control
Now playing
07:26
'What research did you do?': Brown presses GOP lawmaker on election fraud claims
PHOTO: CNN
Now playing
01:42
Acosta describes covering last day of Trump administration
WASHINGTON, DC - FEBRUARY 06: Rep. Alexandria Ocasio-Cortez (D-NY) attends a press conference with Rep. Andy Levin (D-MI) about their new bill called the EV Freedom Act on Capitol Hill on February 6, 2020 in Washington, DC. The EV Freedom Act is a plan to create a nation wide charging infrastructure for electric vehicles. (Photo by Samuel Corum/Getty Images)
WASHINGTON, DC - FEBRUARY 06: Rep. Alexandria Ocasio-Cortez (D-NY) attends a press conference with Rep. Andy Levin (D-MI) about their new bill called the EV Freedom Act on Capitol Hill on February 6, 2020 in Washington, DC. The EV Freedom Act is a plan to create a nation wide charging infrastructure for electric vehicles. (Photo by Samuel Corum/Getty Images)
PHOTO: Samuel Corum/Getty Images
Now playing
03:35
Rioter charged with threatening to 'assassinate' Ocasio-Cortez, officer
Now playing
02:41
Loyal Texas Trump voters want Biden to be less divisive
Now playing
01:16
Sen. Patrick Leahy doubles as a Batman actor
Now playing
01:33
Chuck Schumer announces timeline for Trump impeachment
WASHINGTON, DC - JANUARY 22: U.S. President Joe Biden signs an executive order as Vice President Kamala Harris looks on during an event on economic crisis in the State Dining Room of the White House January 22, 2021 in Washington, DC. President Biden spoke on his administration
WASHINGTON, DC - JANUARY 22: U.S. President Joe Biden signs an executive order as Vice President Kamala Harris looks on during an event on economic crisis in the State Dining Room of the White House January 22, 2021 in Washington, DC. President Biden spoke on his administration's response to the economic crisis that caused by the COVID-19 pandemic and signed two executive orders. (Photo by Alex Wong/Getty Images)
PHOTO: Alex Wong/Getty Images North America/Getty Images
Now playing
02:31
Biden zeroes in on the teetering economy in first week
White House senior adviser Kevin Hassett speaks with reporters at the White House, Friday, June 19, 2020, in Washington. (AP Photo/Alex Brandon)
White House senior adviser Kevin Hassett speaks with reporters at the White House, Friday, June 19, 2020, in Washington. (AP Photo/Alex Brandon)
PHOTO: Alex Brandon/AP
Now playing
05:08
Ex-Trump official who supports Biden stimulus plan speaks out
Dick Durbin 0122
Dick Durbin 0122
PHOTO: CNN
Now playing
01:41
Sen. Durbin: We can't pass anything without bipartisanship
JOINT BASE ANDREWS, MARYLAND - JANUARY 20: President Donald Trump boards Air Force One at Joint Base Andrews before boarding Air Force One for his last time as President on January 20, 2021 in Joint Base Andrews, Maryland. Trump, the first president in more than 150 years to refuse to attend his successor
JOINT BASE ANDREWS, MARYLAND - JANUARY 20: President Donald Trump boards Air Force One at Joint Base Andrews before boarding Air Force One for his last time as President on January 20, 2021 in Joint Base Andrews, Maryland. Trump, the first president in more than 150 years to refuse to attend his successor's inauguration, is expected to spend the final minutes of his presidency at his Mar-a-Lago estate in Florida. (Photo by Pete Marovich - Pool/Getty Images)
PHOTO: Pete Marovich/Pool/Getty Images
Now playing
04:20
Former top administration officials lobby to convict Trump
Guard Soldiers were ordered to move from the cafeteria to the parking garage
Guard Soldiers were ordered to move from the cafeteria to the parking garage
PHOTO: Obtained by CNN
Now playing
01:42
Photos show National Guard confined to parking garage
mccarthy
mccarthy
Now playing
04:18
McCarthy contradicts himself on Trump's role in insurrection
(CNN) —  

President Donald Trump on Wednesday fired Attorney General Jeff Sessions.

“At your request I am submitting my resignation,” Sessions wrote in a letter to White House chief of staff John Kelly.

READ: Jeff Sessions’ resignation letter

Matthew Whitaker will take over as acting attorney general, the President said.

Whitaker is expected to take charge of the Russia investigation and special counsel Robert Mueller from Deputy Attorney General Rod Rosenstein. Whitaker has been openly critical of Mueller and the investigation and Democrats immediately called on him to recuse himself, just as Sessions had.

RELATED: Trump’s replacement for Sessions once argued the Mueller probe goes too far

“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 …We thank Attorney General Jeff Sessions for his service, and wish him well! A permanent replacement will be nominated at a later date,” Trump tweeted.

The move is an abrupt end to what had been a tumultuous tenure for Sessions, originally one of Trump’s earliest and most loyal surrogates as an Alabama Republican senator. He was a key figure in implementing Trump’s vision for America and significantly rolled back Obama-era policies on immigration, police reform and civil rights.

Sessions was an enforcer of much of the Trump administration’s hardline approach on immigration and regularly praised the President’s tough words on crime. But even as he continued to carry out the Trump agenda, his relationship with the President remained strained and fraught for months due to the ongoing Mueller investigation.

Sessions received the request to resign from Kelly, not the President, on Wednesday morning, an administration official said. It is not clear whether Mueller was told ahead of time.

Sessions believed that Rosenstein has handled the investigation properly after it was dropped “right in his lap,” according to a source familiar with Sessions’ thinking.

“[Rosenstein is] a professional, he’s tried to do the right thing and he’s handled it as well as anybody could,” the source said of Sessions’ views on the matter.

However, the source said that Sessions himself has been frustrated that Mueller’s investigation has not yet concluded, but DOJ officials have “tried to do the right thing every day and not be involved in arguing the case in the media.”

In a statement, Whitaker said he will lead a “fair” department with high ethical standards.

“It is a true honor that the President has confidence in my ability to lead the Department of Justice as Acting Attorney General. I am committed to leading a fair Department with the highest ethical standards, that upholds the rule of law, and seeks justice for all Americans,” he said.

Trump constantly criticized Sessions

Sessions’ ouster came a day after the midterm elections saw Republicans hold onto control of the Senate – which would confirm Trump’s eventual permanent choice to head the Justice Department – and just weeks after Trump’s former personal attorney Michael Cohen pleaded guilty to multiple counts of campaign finance violations, tax fraud and bank fraud and Trump’s former campaign chair Paul Manafort was found guilty of eight charges including tax fraud and bank fraud.

RELATED: Trump must reckon with new realities in wake of the election

Sessions was aware that Cohen was facing bank fraud and tax violations but had been walled off from the campaign finance aspects of the investigation into Trump’s former lawyer, a source with direct knowledge of the matter told CNN.

Trump’s distaste for Sessions was well known – and publicly reinforced by the President himself on a regular basis – after the attorney general recused himself from all matters related to the 2016 campaign early in Trump’s term.

RELATED: Trump calls Attorney General Jeff Sessions ‘scared stiff and Missing in Action’

The President mocked Sessions in August as “scared stiff and Missing in Action.” Later the same month as Trump continued to rail against him, Sessions issued a statement firing back at Trump and declaring, “While I am Attorney General, the actions of the Department of Justice will not be improperly influenced by political considerations. I demand the highest standards, and where they are not met, I take action.”

RELATED: Sessions hits back at Trump: DOJ won’t be ‘improperly influenced’

Just days later, Trump knocked the Sessions-led Justice Department for indicting two Trump-supporting Republican congressmen ahead of the midterm elections. Both lawmakers won their re-election bids Tuesday.

But Sessions hung on, and although there was no formal reconciliation, the President allowed him to stay, even despite the unwillingness of White House spokespeople to publicly confirm, for days, that Trump had confidence in the attorney general.

In early August, Trump tweeted that Sessions “should stop” Mueller’s investigation, raising questions as to whether the President was attempting to obstruct justice. Trump’s attorney Rudy Giuliani told CNN’s Dana Bash that Trump was merely “expressing his opinion on his favorite medium.”

Sessions, for his part, consistently maintained that his recusal decision was made in consultation with career ethics officials at the Justice Department and was in the works from the time he was sworn in.

Democrats demand continued independence for Mueller

Top Democrats immediately called for Mueller’s investigation to be allowed to proceed.

Senate Minority Leader Chuck Schumer called on the new acting attorney general to recuse himself from oversight of the Mueller probe.

“Given his previous comments advocating defunding and imposing limitations on the Mueller investigation, Mr. Whitaker should recuse himself from its oversight for the duration of his time as acting attorney general,” Schumer said.

RELATED: Democrats to use House majority to launch Trump investigations

Former Obama administration Attorney General Eric Holder declared interference with the special counsel “a red line.”

“Anyone who attempts to interfere with or obstruct the Mueller inquiry must be held accountable. This is a red line. We are a nation of laws and norms not subject to the self interested actions of one man,” Holder tweeted.

New York Democratic Rep. Jerry Nadler tweeted a vow for accountability. Nadler is poised to chair the House Judiciary Committee next year.

“Americans must have answers immediately as to the reasoning behind @realDonaldTrump removing Jeff Sessions from @TheJusticeDept. Why is the President making this change and who has authority over Special Counsel Mueller’s investigation? We will be holding people accountable,” Nadler tweeted.

Immigration bonded him with Trump from the start

Sessions’ campaign loyalty to Trump earned him a plumb spot in the administration as attorney general, and Sessions’ former aides and allies, including prominent Trump adviser Stephen Miller, spread throughout the administration in key posts across multiple agencies.

Under Sessions, the Justice Department has been aggressive in trying to cut off funds to and punish sanctuary cities – though the courts have repeatedly admonished many of those efforts – and was the primary agency that justified the ending of the Deferred Action for Childhood Arrivals policy, a program that protected young undocumented immigrants who came to the US as children.

Sessions moved to push the limits of his authority over the nation’s immigration system and reinterpreted asylum law as he clashed with immigration judges. He has been the voice of many of the administration’s most aggressive immigration priorities, and was a staunch defender of the administration’s policies last summer that led to the separation of immigrant families and led to widespread outcry.

CNN’s Veronica Stracqualursi and Tal Kopan contributed to this report.