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The chairman of the House intelligence committee has backed down from his dramatic assertion that Donald Trump and his aides were "monitored," by U.S. spies — a claim the Republicans have cited this week in emails to loyalists.

Rep. Devin Nunes told reporters Friday he can’t be sure whether conversations among Trump or his aides were captured in the surveillance that has become a source of controversy since Nunes made it public in two news conferences this week.

"He said he’ll have to get all the documents he requested from the (intelligence community) about this before he knows for sure," his spokesman, Jack Langer, said earlier.

Nunes continued to refuse to say how he had learned about the surveillance, including whether his source was in the White House.

Langer asserted that Nunes did not explicitly say Trump was spied on when he briefed reporters Wednesday that he was "very concerned," that "the intelligence community incidentally collected information about American citizens involved in the Trump transition."

As for Trump’s assertion that Obama wiretapped him, Nunes repeated Friday what he has said previously, telling reporters, "That didn't happen."

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Related: Trump Says He Feels 'Somewhat Vindicated' By Nunes Disclosure

However, Nunes on Wednesday had left an impression — widely repeated in the news media — that the conversations of Trump and his aides were picked up by American spies.

"I have seen intelligence reports that clearly show the president elect and his team were at least monitored and disseminated out," Nunes told reporters.

On Thursday, the Republican Congressional Campaign Committee sent out an email about Nunes' remarks with the subject line, "Confirmed: Obama Spied on Trump."

Nunes himself said he wasn’t making that claim — he said the surveillance was legal and there was no wiretap of Trump Tower. But those sorts of assertions by Republicans raised the question about whether what Nunes did was intended to give Trump cover for his discredited claim that Obama "wiretapped" him.

Current and former officials say that it's possible that Trump or his aides were picked up "incidentally" by surveillance, if a foreign diplomat or other target called them or emailed them. But it is far more likely, they say, that what Nunes was talking about was surveillance of foreigners talking to foreigners, who were speaking about Trump and his aides.

Those conversations were then excerpted in intelligence reports that circulated around the government.

Surveillance of those conversations required warrants from the Foreign Intelligence Surveillance Court if the foreigners are in the United States — as diplomats, for example — or if the communications traverse U.S. cables.

"I think this is overwhelmingly not information from or to an American," former NSA and CIA director Mike Hayden told Chuck Todd Thursday on Meet the Press Daily. "I think this is overwhelmingly information about an American, foreign to foreign, in which they are doing what you would expect them to do."

Related: What Is Incidental Collection?

After any presidential transition, Hayden continued, foreign embassies under surveillance are sending reports back to their capitals analyzing "who's up, who's down."

To the extent that Americans are mentioned in these documents, those names are supposed to be blacked out in any intelligence report that is circulated around the government, unless the identities are needed to understand the intelligence.

That issue appears to be what Nunes is now focusing on. In some of the intelligence reports he reviewed, Nunes said, the names of Trump aides were blacked out, but he could figure them out anyway. In other reports, he said, the names had been "unmasked," and he questioned whether that was appropriate.

Hayden, a Republican, suggested it might have been done to better understand the intelligence.

"You need to put flesh in there," he said.