Senate Minority Leader Charles Schumer said Sunday that Democrats might tie their support for the next spending bill to legislation that would protect special counsel Robert Mueller – although he stopped short of saying he would be willing to risk a shutdown.

The New York Democrat said President Donald Trump's choice of Matthew Whitaker to head the Justice Department could threaten Mueller's investigation into Russian election meddling and potential ties to the Trump campaign. Trump named Whitaker as the interim attorney general after Jeff Sessions' ouster last week.

"The appointment of Mr. Whitaker should concern every American – Democrat, Republican, liberal, conservative – who believes in rule of law and justice," Schumer said during an interview Sunday on CNN's "State of the Union." "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 cited Whitaker's public comments that he does not believe Russia interfered in the 2016 election and that the funding to Mueller's inquiry should be cut as examples of why Whitaker should not be in charge of the special counsel's investigation.

He said Democratic leaders in the House and Senate plan to send a letter to the chief ethics officer of the Justice Department asking for an opinion on whether Whitaker should recuse himself from the investigation.

If Whitaker does not recuse, Schumer said, Democrats in both houses of Congress 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."

"State of the Union" host Jake Tapper pointed out that Senate Majority Leader Mitch McConnell, R-Ky., indicated he wouldn't support legislation to protect Mueller. Tapper asked Schumer if Democrats would risk a shutdown and refuse to sign a spending bill that didn't include protection for Mueller.

"Look, 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 replied. If Republican support fails to materialize, "we'll see what happens down the road," he said.

He noted that McConnell said he didn't think such legislation was necessary before Sessions was fired because there was no concern that Mueller's investigation would be interfered with when Deputy Attorney General Rod Rosenstein oversaw it.

"With Whitaker, there is every reason to believe there will be interference, based on what Mr. Whitaker has said. The world has changed from when Rosenstein was in charge of the investigation, and I think, I believe, that many Republicans will find the same," Schumer said.

McConnell repeated his position Friday that legislation to protect Mueller would not be brought to the full Senate for a vote after outgoing Sen. Jeff Flake, R-Ariz., called for such a bill.

"It's not going to come up because it isn't necessary," McConnell said in Frankfort, Kentucky.

"The Mueller investigation is not under threat. The president has said repeatedly he's not going to dismiss the Mueller investigation," McConnell said. He said the president had the authority to appoint Whitaker, whom he expected to be a "very interim" attorney general.

Rep. Jerrold Nadler, D-N.Y., who is likely to take over the powerful House Judiciary Committee in January, told Tapper that protecting Mueller from Whitaker, whom he derided as a "complete political lackey," will be his top priority.

Nadler said Whitaker would be the "very first witness after Jan. 3" – when the new Congress begins – after being summoned or, if necessary, subpoenaed, to address how he could supervise Mueller when he has said "the investigation is invalid."

Nadler said Whitaker is "totally unqualified" to lead the Justice Department and Trump wants him in charge only "to be the hatchet man to destroy the Mueller investigation."

Rep. Adam Schiff, who will probably become chairman of the House Intelligence Committee, said Sunday on "Meet the Press" that the case for Whitaker's recusal from the Mueller investigation is "very strong."

The California Democrat warned Whitaker that "if he has any involvement whatsoever in this Russia probe, 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 he plays will be exposed to the public," Schiff said.

On CNN, Tapper asked Nadler and Schumer if they believed the president should be impeached. Both Democrats said they would wait for the results of Mueller's report before making that determination.

Nadler said that for impeachment to move forward, the evidence against Trump would have to be so overwhelming that even many Republicans would agree it was necessary.

Otherwise, "half the country says for the next 30 years, 'We won the election, you stole it.' "

Nadler denied media reports that he was considering impeachment proceedings against Supreme Court Justice Brett Kavanaugh, who Nadler suggested gave false testimony during his confirmation hearings. Nadler said he supported an inquiry into whether the FBI was able to conduct a thorough investigation into sexual assault allegations that Kavanaugh denied.

On "Meet The Press," Schiff conceded that there was a risk that the new Democratic majority in the House could overreach by conducting inquiries into the president.

"Our strongest purpose here is to put forward a positive agenda, and we don't want that lost in a flurry of investigations," he said. Schiff said House Democrats would have to "ruthlessly prioritize" their investigations.

Contributing: Tom Loftus, LouisvilleCourier Journal