WASHINGTON — Republican lawmakers reacted to news of Attorney General Jeff Sessions’ resignation with little surprise, while Democrats vowed to use their new House power in the upcoming Congress to dig into the president’s reason behind the move.

President Trump tweeted the news after his press conference, several hours after a tweet calling special counsel Robert Mueller’s investigation into Russia’s campaign influence operation a “witch hunt.”

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

Whitaker, U.S. Attorney for the Southern District of Iowa during the George W. Bush administration, vied for the GOP Senate nomination in Iowa in 2014 but lost to Sen. Joni Ernst (R-Iowa). In August 2017, he wrote a CNN op-ed arguing that “Mueller has come up to a red line in the Russia 2016 election-meddling investigation that he is dangerously close to crossing” by reportedly looking into Trump’s finances. He also made comments on TV about how Trump could starve the Mueller investigation of resources, and in 2014 led the unsuccessful campaign of Sam Clovis, Trump’s 2016 campaign co-chairman, for Iowa state treasurer; Clovis is now a grand jury witness in the Mueller probe.

Senate Minority Leader Chuck Schumer (D-N.Y.) said in a statement this afternoon that “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.”

“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 (D-Calif.) 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.”

Rep. Jerry Nadler (D-N.Y.), expected to be the incoming chairman of the House Judiciary Committee, tweeted, “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.”

In his resignation letter, Sessions said he was resigning at the president’s request and expressed his gratitude to law enforcement. “In my time as attorney general we have restored and upheld the rule of law — a glorious tradition that each of us has a responsibility to safeguard,” Sessions wrote. “We have operated with integrity and have lawfully and aggressively advanced the policy agenda of this administration.”

Senate Majority Leader Mitch McConnell (R-Ky.) issued a statement thanking Sessions for “his dedicated service as attorney general.”

“Throughout his career, as a prosecutor, a Senator and as Attorney General, he remained steadfast in his commitment to the rule of law and his love of our great nation,” McConnell said. “I wish him well and look forward to working with him in any future endeavors.”

Senate Majority Whip John Cornyn (R-Texas) said that “those who know him understand his commitment to the rule of law, and his deep and abiding concern for our country.”

Sen. Tim Scott (R-S.C.) said he is “hopeful that President Trump will take this opportunity to nominate a replacement that is invested in criminal justice reform — in addition to being the top lawyer in the land, the AG is uniquely placed to lead our nation forward on this important issue.”