Senate Minority Leader Chuck Schumer, D-N.Y., said that if Acting Attorney General Matt Whitaker does not recuse himself from oversight of Special Counsel Robert Mueller's Russia probe, then Democrats will seek to tie protections for the investigation into the spending bill.

"We Democrats, House and Senate, will attempt to add to must-pass legislation, in this case the spending bill, legislation that would prevent Mr. Whitaker from interfering with the Mueller investigation" should Whitaker not recuse, Schumer said Sunday during an appearance on CNN's "State of the Union."

Schumer said he was concerned about the past statements Whitaker made as a commentator on CNN about the investigation. Whitaker has argued that cutting Mueller’s budget would be a way to end the probe, that investigating President Trump’s finances would be a “red line” and that he believes there was "no collusion" between Russia and the Trump campaign.

"The appointment of Mr. Whitaker should concern every American – Democrat, Republican, liberal, conservative – who believes in rule of law and justice," Schumer said." "He has already prejudged the Mueller situation. If he stays there, he will create a constitutional crisis by inhibiting Mueller or firing Mueller, so Congress has to act."

Schumer, along with House Minority Leader Nancy Pelosi, D-Calif., and other key Democrats, are sending a letter to Lee Lofthus, the top ethics officer at the Justice Department, to question Lofthus if he had advised Whitaker to recuse himself from oversight of the Mueller probe.

Schumer, however, stopped short of saying he would risk a government shutdown if Mueller protection’s weren’t added to a spending bill.

“I believe there will be enough of our Republican colleagues who will join us. There's no reason we shouldn't add this and avoid a constitutional crisis," Schumer said. "We'll see what happens down the road.”

With the pushback from top Democrats, numerous Republican lawmakers have come to Whitaker's defense. Sen. Lindsey Graham, R-S.C., said Whitaker was "appointed legally" and there was no reason for him to recuse himself from the Mueller investigation.

"You don't recuse somebody because they have opinions different than the people they're overseeing," Graham said Sunday on CBS' "Face the Nation." "The bottom line here is Mueller will be allowed to do the job without political interference by Mr. Whitaker."

Rep. Jerry Nadler, D-N.Y., who is likely to take over as chairman of the House Judiciary Committee come January, said on Sunday that if Whitaker doesn’t recuse himself from overseeing the Mueller investigation, then the acting attorney general will be subpoenaed by the panel.

"Our very first witness after January 3, we will subpoena, or we will summon, if necessary subpoena, Mr. Whitaker," Nadler said on “State of the Union.” “The questions we will ask him will be about his expressed hostility to the investigation.”

Nadler added: “How he can possibly supervise it when he's expressed, when he's come out and said that the investigation is invalid.”

The ranking Democrat on the House Judiciary Committee said that protecting Mueller’s investigation will be a top priority should he take over as the panel’s chair come January.

"Well, the very first thing, obviously, is to protect the Mueller investigation. The President's dismissal of Attorney General Sessions and his appointment of Whitaker, who's a complete political lackey, is a real threat to the integrity of that investigation," he said, adding that the investigation is "of utmost importance."