"I'll say something even more concerning to me, and that is the intelligence community is beginning to withhold documents from Congress on the issue of Ukraine. They appear to be succumbing to pressure from the administration," Schiff, the House Intelligence Chairman, told ABC.

"The NSA in particular is withholding what are potentially relevant documents to our oversight responsibilities on Ukraine, but also withholding documents potentially relevant that the senators might want to see during the trial," Schiff continued, referring to Trump's upcoming trial. "That is deeply concerning."

The California Democrat said there "are signs that the CIA may be on the same tragic course." Schiff, however, did not elaborate on those "signs," or specify during the aired interview what documents are being withheld.

The National Security Agency has not responded to CNN's request for comment.

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