Following months of speculation, President Donald Trump canned his embattled Attorney General Jeff Sessions and replaced him in the interim with Sessions’ chief of staff, Matthew Whitaker, immediately raising concerns that the Special Counsel Robert Mueller’s investigation into Russian interference and potential collusion with the Trump campaign is in jeopardy.

“At your request I am submitting my resignation,” Sessions wrote in a letter to Trump, noting that he had worked “to support the fundamental legal processes that are the foundation of justice.”

The president had long derided Sessions, blaming him for Mueller’s probe, after the attorney general recused himself from overseeing a Russian investigation then headed up by former FBI Director James Comey, instead passing oversight to Deputy Attorney Rod Rosenstein. It was Trump’s firing of Comey – ostensibly for the way he handled the Hillary Clinton email investigation although the president admitted later that Comey was ousted over the Russian probe – that prompted Rosenstein to appoint the special counsel.

That investigation and its offshoots have led to multiple indictments and guilty pleas not only of Russian operatives and organizations but also of those once in Trump’s inner circle, including former Campaign Director Paul Manafort, former Deputy Campaign Rick Gates and former campaign adviser George Papadopoulos, and has brought close scrutiny to the actions of family members Donald Trump, Jr. and son-in-law Jared Kushner.

The president has said he’d let the investigation run its course but has regularly expressed frustration with what he calls a “witch hunt” and hinted that he wants it wrapped up.

“We are deeply concerned that Trump is again trying to interfere with the Trump-Russia investigation by forcing Sessions’ resignation,” said CREDO Action Co-Director Heidi Hess. Any interference with Robert Mueller’s investigation would be completely unacceptable.”

For two years critics have voiced concern that Trump would get rid of Sessions and appoint an attorney general that would be willing to fire Mueller or at least curb his probe.

Democrats, who won back the House the day before news broke on Sessions’ ouster, said they would look into the action.

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

In the days leading up to the midterm elections, speculation ran high that Mueller would soon issue a new round of indictments that would bring his investigation even closer to the president.

Trump critic Rep. Adam Schiff, D-Calif., took to Twitter to claim the president “wants an Attorney General to serve his interest, not the public. Mueller’s investigation and the independence of the DOJ must be protected. Whitaker and any nominee must commit to doing both. We will protect the rule of law.”

Interim Attorney General Whitaker, who a Justice Department spokesperson told the press would be overseeing all matters of the Justice Department, once wrote that the Mueller probe had gone too far when it expanded to include the Trump Organization’s financials. “Mueller has come up to a red line in the Russia 2016 election-meddling investigation that he is dangerously close to crossing,” he wrote.

However, that was before the special counsel had indicted multiple parties and laid the groundwork to possibly expose a financial web that helped fund Russia’s exploits during the 2016 election. 

Whitaker also rebuffed criticism of Trump, Jr.’s Trump Tower meeting with a Russian lawyer offering “dirt” on Clinton, saying, “You would always take that meeting.”

“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,” Sen. Chuck Schumer, D-N.Y., tweeted.