Sen. John McCain John Sidney McCainMcSally says current Senate should vote on Trump nominee Say what you will about the presidential candidates, as long as it isn't 'They're too old' The electoral reality that the media ignores MORE (R-Ariz.) on Tuesday said House Intelligence Committee Chairman Devin Nunes (R-Calif.) needs to explain his visit to White House grounds one day before briefing President Trump on surveillance affecting his transition team.

"I think there needs to be a lot of explaining to do,” McCain told “CBS This Morning.” “I’ve been around for quite a while and I’ve never heard of such thing.”

Nunes has come under fire from Democratic lawmakers after admitting on Monday that he visited White House grounds last week to meet with a source and view classified material. One day after that visit, Nunes briefed Trump and told reporters that intelligence on Trump transition team members had incidentally been collected.

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Nunes has maintained that the material in question was not related to Russia or the committee’s investigation into Russia’s interference in last year's U.S. presidential election.

McCain said Nunes should "absolutely" reveal his source.

McCain also said the House Intelligence Committee’s investigation into Russia must be bipartisan to be credible.

“There’s so much out there that needs to be explained by the chairman,” McCain said.