House Intelligence Committee Chairman Rep. Devin Nunes, R-Calif. pauses while speaking with reporters outside the White House in Washington, Wednesday, March 22, 2017, following a meeting with President Donald Trump. AP Photo/Pablo Martinez Monsivais The revelation that the chairman of the House Intelligence Committee, Devin Nunes, was on White House grounds the day before he briefed President Donald Trump on documents related to surveillance of his transition team has fueled speculation that the White House itself was Nunes' source.

Nunes, who was a member of Trump's transition team, told Fox on Tuesday afternoon that he would "never reveal" the source of the classified documents he obtained, not even to other members of the House Intelligence Committee.

Nunes on Monday said he had gone to the White House last week to view the documents because Congress didn't have "networked access" to those reports.

His spokesman later told Business Insider that Nunes had been there to view the documents in a secure compartmented information facility, or SCIF, to "safeguard the proper chain of custody and classification of these documents," but did not respond when asked why an executive branch source would not go directly to Trump, instead of to Nunes, with documents they found suspicious.

Nunes has insisted that no one from the Trump administration knew he was on White House grounds being briefed on the documents. But national-security experts, Republican and Democratic members of Congress, and White House reporters have said it is highly unlikely Nunes could have gone unnoticed on White House grounds.

"This is insane," Juliette Kayyem, a CNN national-security analyst and former official at the Department of Homeland Security, told Business Insider on Monday. "You only go to the White House to get briefed by the White House. It's not a meeting point like a McDonald's off the turnpike."

Democratic Rep. Eric Swalwell, a member of the House Intelligence Committee, echoed Kayyem's assessment on Tuesday morning. The White House "is not an internet café," Swalwell told MSNBC. "You can't just walk in and receive classified information."

Swalwell also wondered why Nunes couldn't have viewed the documents inside an SCIF at the Capitol after consulting with his fellow committee members.

"If this was done the proper way, they could have brought it over, shared it with both parties of the committee," he said, referencing what he said was the bipartisan nature by which intelligence-committee investigations are typically conducted.

If you're a member of Congress visiting the White House, "everyone in the building knows that you're there in the building," Swalwell said. "This is what a cover-up to a crime looks like."

"None of us, Democrat or Republican, on the Senate Intelligence Committee still has any idea what [Nunes is] talking about," Sen. Mark Warner, the committee's ranking Democrat, told reporters on Tuesday. "I don't believe, frankly, the members, Republican or Democrat, on the House committee do either."

Rep. Adam Schiff, left, the ranking member of the House Intelligence Committee, and Nunes, the chairman. Drew Angerer/Getty Images

"To come onto these grounds at the White House, you must be authorized," Jeff Zeleny, CNN's senior White House correspondent, said on Tuesday. "Someone invited him in, cleared him in, escorted him in. This White House has made the decision to not say who that was."

Republican Sen. John McCain agreed that Nunes' move was unusual.

"I've been around for quite a while, and I've never heard of any such thing," he said on Tuesday morning on CBS.

White House press secretary Sean Spicer said on Tuesday that while he didn't know who Nunes spoke to, any conversations the congressman had with a source — assuming that person had security clearance — were "100% legal" and "completely appropriate."

The day after he went to the White House, Nunes announced in an unexpected press conference that the president and his advisers may have had their communications "incidentally collected" by the intelligence community during the transition period.

Nunes said the reports he had seen had nothing to do with Russia, which is why he felt comfortable briefing Trump on the matter without first informing the ranking member of the House Intelligence Committee, Democratic Rep. Adam Schiff.

Schiff joined a growing chorus of Democrats calling for Nunes to recuse himself from the committee's investigation into whether the Trump campaign colluded with Russia, saying in a statement that "none of the committee members — Democrats or Republicans — has seen the relevant documents, now almost a week later."

"There was no legitimate justification for bringing that information to the White House instead of the committee," Schiff added. "That it also obtained at the White House makes this departure all the more concerning."