Adam Schiff, the top Democrat on the House Intelligence Committee, called for its chairman, Rep. Devin Nunes, to recuse himself from "any investigation" into President Donald Trump's campaign and transition team after news of the Republican's secret White House meeting on the issue emerged.

“This is not a recommendation I make lightly,” Rep. Adam Schiff wrote in a statement of his counterpart on the committee investigating Russia's inference in the 2016 election. “I believe the public cannot have the necessary confidence that matters involving the President’s campaign or transition team can be objectively investigated or overseen by the Chairman.”

The call comes hours after Nunes acknowledged reports that he went to the White House the day before he made the explosive claim that Trump and his associates may have been “incidentally” swept up in foreign surveillance by American spy agencies, offering what some said was a sliver of credence to the president's still unsubstantiated theory that he was wiretapped by his predecessor.

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"Enough question has been raised in the public about whether he can lead a credible investigation in this, given the severity of the issues," Schiff told reporters Monday night.

Nunes would not say publicly who his source on the claim was, but he rankled the committee he leads by briefing the House Speaker Paul Ryan and the White House before telling the Democrats on his committee what he'd seen. Now, news that the source meeting was on the White House grounds has fueled suspicion that it could have been someone close to the president.

Nunes later walked back his claim that the president was monitored, saying he couldn’t be sure that communications between the president and his team were captured, but not before the president said he felt "somewhat vindicated" by Nunes' announcement.

Related: Nunes Had Secret White House Meeting Before Trump Monitoring Claim

Nunes said he was at the White House to meet with a source and view classified documents, but did not explain why he wouldn’t use the classified document-viewing space available on Capitol Hill. He also claimed that the White House did not know he was there.

Schiff noted in his statement Monday that he and the rest of the Intelligence Committee have yet to see the documents Nunes said proved the surveillance.

The claim of Trump and his team being incidentally surveilled is “impossible to judge," Schiff said. "But one thing is very clear: There was no legitimate justification for bringing that information to the White House instead of the committee. That it was also obtained at the White House makes this departure all the more concerning.”

House Minority Leader Nancy Pelosi echoed Schiff, calling on House Speaker Paul Ryan to insist on Nunes step aside.

“Speaker Ryan must insist that Chairman Nunes at least recuse himself from the Trump-Russia investigation immediately. That leadership is long overdue,” Pelosi said in the statement.