Eric Swalwell, the California Democrat. Marcio Jose Sanchez/AP Photo

Democratic Rep. Eric Swalwell, who sits on the House Intelligence Committee, laid into committee chair Devin Nunes on Tuesday, alleging that Nunes had breached protocol when he viewed classified documents on White House grounds.

The White House "is not an internet café. You can’t just walk in and receive classified information," Swalwell said on MSNBC's "Morning Joe" show.

Nunes said Monday that he had been on White House grounds when he met with an unnamed source who provided him with documents that he claims show evidence that Trump and his associates may have had their communications "incidentally collected" by the intelligence community during the transition period.

The next day, he briefed the president on the information he had received before briefing members of his committee.

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

Nunes' announcement ignited a firestorm, as Democrats on the committee wondered why he had viewed the documents at the White House instead of the Capitol, as well as why he went to the president before briefing the rest of the committee. Several Democrats on and outside of the committee — including ranking member Adam Schiff — called on Nunes to recuse himself from the committee's investigation into Trump's connections with Russia.

"Because of classification rules, the source could not simply put the documents in a backpack and walk them over to the House Intelligence Committee space," Nunes' spokesman, Jack Langer, said on Monday. "The White House grounds was the best location to safeguard the proper chain of custody and classification of these documents so the chairman could view them in a legal way."

Swalwell disputed Nunes' statement, saying that there were secure facilities at the Capitol where Nunes could have viewed the intel he had received about the president and his associates.

"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.

Devin Nunes, the Republican chairman of the House Intelligence Committee. AP

Swalwell also expressed disbelief toward Nunes' assessment that people in the West Wing "had no idea" he'd been on White House property.

When a congressional member visits, Swalwell said, "Everyone in the building knows that you’re there in the building.

"This is done because the White House wanted it to be done," he said. "And this is what a cover-up to a crime looks like. We are watching it play out right now."

Democrats on the committee have called for Nunes to step down as chair and to recuse himself from the investigation. Some have called for an independent investigation into the president's ties to Russia.

"After much consideration, and in light of the chairman's admission that he met with his source of information at the White House, I believe that the chairman should recuse himself from any further involvement in the Russia investigation, as well as any involvement in oversight of matters pertaining to any incidental collection of the Trump transition, as he was also a key member of the transition team," Schiff said in a statement.

Rep. Jackie Speier, a Democrat who sits on the committee, said in a statement that her "fears have been validated" by the developments in recent days.

"Through his bizarre and partisan actions over the last week," she said, "Chairman Nunes has demonstrated to the entire nation why he is unfit to lead our critical investigation into ties between President Trump's administration and Moscow."