(CNN) -- Key House Democrats are calling on Intelligence Committee Chairman Devin Nunes to recuse himself from an investigation into alleged ties between the Trump campaign and Russia, widening a stunning partisan split over the probe.
"The Chair of the House Intelligence has a serious responsibility to the Congress and to the country," House Minority Leader Nancy Pelosi said in a statement to CNN Monday evening. "Chairman Nunes' discredited behavior has tarnished that office. (House) Speaker (Paul) Ryan must insist that Chairman Nunes at least recuse himself from the Trump-Russia investigation immediately. That leadership is long overdue."
Her request came a little more than an hour after Rep. Adam Schiff, the committee's top Democrat, requested Nunes' recusal.
"We've reached the point, after the events of this week, where it would be very difficult to maintain the credibility of the investigation if the chairman did not recuse himself from matters involving either the Trump campaign or the Trump transition team of which he was a member," Schiff told CNN on Monday.
"The questions are profound enough that I think we need to move past it, and ideally that would mean the chairman ought to recuse himself, not only from the investigation involving potential coordination or collusion between the Trump campaign and the Russians, but also any oversight of minimization issues affecting the Trump transition since he was a member of that Trump transition team."
Nunes, however, told CNN Tuesday morning he was "moving forward" with the investigation.
Pelosi and Schiff's requests Monday followed a meeting of the Democrats on the House Intelligence Committee, a panel typically seen as more above the political fray than other committees in the House. Two sources on the committee told CNN the panel has scrapped all meetings this week amid the partisan rancor.
Ryan still supports Nunes, spokeswoman AshLee Strong said Monday, and will not ask him to recuse himself.
"Speaker Ryan has full confidence that Chairman Nunes is conducting a thorough, fair, and credible investigation," Strong said.
The request for recusal marks a critical split between Schiff and Nunes, who had worked closely on the House investigation into ties between top aides to the campaign of President Donald Trump and Russian officials.
It comes just hours after CNN reported that Nunes visited the White House grounds one day before going to the President with evidence that his transition aides' communications were picked up in surveillance by US intelligence.
"This is not a recommendation I make lightly, as the chairman and I have worked together well for several years; and I take this step with the knowledge of the solemn responsibility we have on the Intelligence Committee to provide oversight on all intelligence matters, not just to conduct the investigation," Schiff said Monday.
Nunes defended his handling of the investigation as well as his relationship to the White House during an interview with CNN's Wolf Blitzer Monday.
"The Congress has not been given this information, these documents, and that's the problem," Nunes said on CNN's "The Situation Room," explaining why he went to the White House. "This is Executive Branch."
Rep. Joaquin Castro, in an interview Monday evening with CNN's Erin Burnett on "OutFront," echoed Schiff's call.
"Actions taken by the chairman have compromised the investigation," Castro said. "Chairman Nunes at this point should recuse himself from this investigation."
He said Nunes, who was a member of Trump's transition team, was too invested in Trump's political agenda, and acting in a partisan way.
"I understand that for members of Congress, there is of course an inclination to help a President who's of your party," Castro said. "You simply can't do that. ... You have to be able to separate yourself from that."
Republican Sens. Lindsey Graham and John McCain -- two frequent critics of the Trump administration and Russia -- joined in criticism of Nunes Tuesday morning, though they stopped short of calling for the chairman to recuse himself.
Graham told NBC's "Today" show that Nunes "has to repair the damage," though he added that "the House is off track and probably can't get back on track."
"If he's not willing to tell the Democrats and the Republicans on the committee who he met with and what he was told, he has lost his ability to lead," Graham said, "and the Democrats on the committee are becoming prosecutors."
And McCain said Nunes needs to provide more answers.
"I think there needs to be a lot of explaining to do. I've been around for quite a while and I've never heard of any such thing," the Arizona Republican said on CBS's "This Morning," referring to Nunes' White House visit. "Obviously, in a committee like an intelligence committee, you got to have bipartisanship otherwise the committee loses credibility. And so there's so much out there that needs to be explained by the chairman."
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