Senate Democratic Leader Chuck Schumer demanded Monday that Rep. Devin Nunes be replaced as head of the House Intelligence Committee to ensure a “credible” investigation into alleged ties between Russian officials and the Trump campaign.

“If Speaker [Paul] Ryan wants the House to have a credible investigation, he needs to replace Chairman Nunes,” Schumer said on the Senate floor.

“Chairman Nunes is falling down on the job and seems to be more interested in protecting the president than in seeking the truth. You cannot have the person in charge of an impartial investigation be partial to one side. It’s an inherent contradiction.”

Schumer’s demand came after Nunes said Monday he met with a source on the White House grounds a day before announcing that members of Team Trump had “incidentally” been caught in surveillance by US agencies.

In a statement, Nunes’ spokesman Jack Langer said he used the grounds “in order to have proximity to a secure location where he could view information provided by the source.”

Nunes, (R-Calif.) told CNN on Monday that he had been on the grounds “to confirm what I already knew,” but declined to elaborate so he wouldn’t “compromise sources and methods.”

Nunes, whose committee is investigating Russia’s interference in the 2016 presidential election, told reporters last Wednesday that he had information that showed Trump and his aides may have been swept up in surveillance of foreign government officials by US spy agencies.

He was criticized for taking the unusual step of bypassing members of his House committee before briefing Trump on the information and for the timing of the announcement.

It came a day after FBI Director James Comey told Nunes’ panel that his agency was investigating possible “coordination” between Trump aides and Moscow. Comey also said he had no evidence to support Trump’s allegation that former President Trump authorized the wiretapping.

“What I’ve read bothers me, and I think it should bother the president himself and his team,” Nunes said outside the White House on Wednesday.

At the White House press briefing on Monday, spokesman Sean Spicer said he isn’t aware where Nunes got his information.

“I know in his public statement, he has talked about having multiple sources,” Spicer said.

Pressed that it came from inside the White House, Spicer said he couldn’t be “100 percent” certain, adding “Anything’s possible.”

Nunes, who was part of Trump’s transition team, said the monitoring was not connected to Russia and couldn’t provide evidence supporting the president’s claim that he was personally wiretapped at Trump Tower.

He wouldn’t tell reporters who provided the intelligence reports and identified them only as people who had security clearances.

Afterward, Trump said the revelations “somewhat” vindicated him.

“I very much appreciated the fact that they found what they found,” the president said.

The ranking Democrat on the Senate Intelligence Committee, which is also investigating Russia’s involvement in the election, said Nunes’ visit is “more than suspicious.”

“Who is he meeting with?” Sen. Mark Warner (D-Va.) told Politico on Monday. “Was it a source or was it somebody from the administration? And then he goes through this, what appears to be a charade, where he comes out the next day and briefs the president before he tells the Democrats.”

Late Monday, Ryan’s office issued a statement saying Nunes isn’t being replaced.

“Speaker Ryan has full confidence that Chairman Nunes is conducting a thorough, fair and credible investigation,” said Ryan spokeswoman AshLee Strong.