Democratic lawmakers on Sunday demanded assurances from the Justice Department that acting Attorney General Matthew Whitaker will recuse himself from overseeing Special Counsel Robert Mueller's investigation into President Donald Trump's 2016 campaign, calling a failure to do so a clear breach of ethics.

In a letter (pdf) to the department's top ethics official, Democrats who are expected to wield subpoena power in the upcoming congressional session wrote that Whitaker's well-documented history of hostility towards the Mueller probe amounts to a clear conflict of interest, and necessitates a recusal in the same way former Attorney General Jeff Sessions' own meetings with Russians during the 2016 campaign did.

"There are serious ethical considerations that require Mr. Whitaker's immediate recusal from any involvement with the Special Counsel investigation," wrote the Democrats. "The official supervising the Special Counsel investigation must be—in both fact and appearance—independent and impartial. Regrettably, Mr. Whitaker's statements indicate a clear bias against the investigation that would cause a reasonable person to question his impartiality."

Among the seven signers of the letter to Lee Lofthus, Assistant Attorney General for Administration, were Reps. Jerry Nadler (D-N.Y.) and Adam Schiff (D-Calif.). Nadler is expected to take control of the House Judiciary Commitee in January while Schiff will chair the House Intelligence Committee.

Both congressmen spoke with the press on Sunday about their plans to ensure that Whitaker's stated views about the Mueller probe do not interfere with or even shut down the investigation.

"We have every right to expect all of the employees of the Justice Department to follow the ethics rules and that means especially the attorney general," Schiff told Chuck Todd on NBC's "Meet the Press" on Sunday. "We are going to find out whether he made commitments to the president about the probe, whether he is serving as a back channel to the president or his lawyers about the probe, whether he's doing anything to interfere with the probe. Mr. Whitaker needs to understand that he will be called to answer. And any role that he plays will be exposed to the public."

On CNN's "State of the Union," Nadler stated unequivocally that his first priority as the incoming chairman "is to protect the Mueller investigation" and said Whitaker's failure to recuse himself will result in a subpoena.

"The president's dismissal of Attorney General Sessions, and his appointment of Whitaker, who is a complete political lackey, is a real threat to the integrity of that investigation," Nadler told Jake Tapper.

"We will subpoena...Mr. Whitaker," he added.

According to the Washington Post, Whitaker currently has no intention of recusing himself from supervising the investigation.

Before becoming Sessions' chief of staff at the DOJ in 2017, Whitaker was a conservative commentator for CNN, where he wrote an op-ed in August 2017 entitled "Mueller's Investigation of Trump Is Going Too Far."

Whitaker, the Democrats noted, also has close ties with former Trump campaign chairman Sam Clovis, a grand jury witness in the Mueller probe, having served on Clovis's campaign to be Iowa's state treasurer in 2014.

"Mr. Whitaker's relationship with Mr. Clovis, who is a grand jury witness in the Special Counsel investigation, as well as Mr. Whitaker's other entanglements, raise additional concerns about his ability to supervise the investigation independently and impartially," wrote the lawmakers.