Story highlights Rep. Devin Nunes is chairman of the House Intelligence Committee

The ranking member of the committee called on Nunes to recuse himself from a Russia investigation

(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.

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"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."

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