(Bastien Inzaurralde/The Washington Post)

The chairman of the House Intelligence Committee on Wednesday accused U.S. spy agencies of abusing their surveillance powers by gathering and sharing information about President Trump and his transition team, an unproven charge that was quickly embraced by the White House but threatened to derail the committee’s investigation of possible Trump campaign ties to Russia.

Rep. Devin Nunes (R-Calif.), one of Trump’s closest allies on Capitol Hill, said he was alarmed after seeing intelligence reports disseminated after the Nov. 8 election that made references to U.S. citizens affiliated with Trump, and possibly the president-elect himself. He appeared to be referring to relatively routine cases of surveillance on foreign individuals in which they communicated with or mentioned Americans.

“What I’ve read seems to me to be some level of surveillance activity — perhaps legal, but I don’t know that it’s right,” Nunes said to reporters outside the White House. “I don’t know that the American people would be comfortable with what I’ve read.”

But Nunes’s refusal to disclose how he had obtained the documents and his unusual handling of the material — which he withheld from other committee members even while rushing to present it to the White House — were interpreted by some as a sign that his discovery was engineered to help the White House.

Trump said he regarded Nunes’s disclosures as validation of his widely discredited claim that he was the illegal target of a wiretapping operation last fall ordered by President Barack Obama. Asked whether he felt vindicated, Trump said during a brief public appearance at the White House: “I somewhat do. I must tell you I somewhat do. I very much appreciated the fact that they found what they found.”

The timing of Nunes’s disclosures was politically advantageous for Trump, coming just days after FBI Director James B. Comey testified that the president’s wiretapping claims were groundless and falling on a day when Republicans struggled to muster enough votes to pass a health-care overhaul bill.

Nunes’s White House visit was denounced by Democrats as a partisan move that severely damaged the prospects of the committee carrying out an impartial probe.

Rep. Adam B. Schiff (D-Calif.), the ranking Democrat on the House Intelligence Committee, said that Nunes’s action “casts quite a profound cloud over our ability to do the work,” and he called for the formation of an independent commission. “If the chairman is going to continue to go to the White House rather than his own committee, there’s no way we can conduct this investigation.”

Other Democrats suggested that Nunes may have crossed a legal line by publicly talking about secret intelligence work.

Sen. Ron Wyden (D-Ore.) said the congressman’s statements “appear to reveal classified information, which is a serious concern. With regard to the substance of his claims, I have no idea what he is talking about.’’

Nunes, who served as a member of Trump’s transition team, would not say whether his information came from a source affiliated with the White House — or whether the reports he had seen simply cited cables between foreign entities or direct communications between Trump or his team and a foreign agent.

“I’m not going to get into any of this,” he said, stressing only that it was “very clear to me” who the Trump team officials referenced in the report were.

(The Washington Post)

The White House has previously enlisted Nunes, as well as a senior U.S. intelligence official, to knock down politically damaging reports about Trump and Russia. White House officials dismissed suggestions that Trump aides had coordinated with Nunes.

“We watched his press conference on the Hill at the same time everybody else did,” White House deputy press secretary Sarah Sanders said. “We didn’t have any information before that.”

The developments added to the intrigue and animosity that have so far characterized Trump’s relationship with U.S. intelligence agencies, as well as the administration’s efforts to fend off reports of Russian ties that forced the resignation of Trump’s first national security adviser, Michael Flynn, and a recusal on Russia-related matters by Attorney General Jeff Sessions.

Nunes’s claims raise the possibility that U.S. spy agencies violated long-standing rules that are designed to protect U.S. citizens from surveillance and require Americans’ names to be stricken from intelligence reports except in rare circumstances. But the lack of detail provided by Nunes, and the ambiguous wording he used in his public appearances to describe the materials, made it hard to determine whether there was any violation.

Nunes’s statements appear to center on surveillance approved by the Foreign Intelligence Surveillance Court, a secretive panel that authorizes the interception of communications of known or suspected agents of foreign powers — such as ambassadors — or terrorism suspects.

Though it is generally not acknowledged, the U.S. government has for years used FISA warrants to eavesdrop on ambassadors, embassies and others believed to be acting in America on behalf of foreign governments.

While such surveillance aims to gather intelligence about foreign actors, it can often pick up conversations with their American counterparts — such as State Department officials, lawmakers or other Americans who speak to foreign officials. Agencies refer to such monitoring as “incidental’’ collection and take steps to minimize the sharing of those people’s names or identifying information within the government, often by masking their names in internal reports about the intercepted communications.

Nunes described the surveillance as apparently legal but nevertheless troubling because it involved the activities of Trump and his aides after he was elected but before he became president.

“It looks to me like it was all legally collected. It was a lot of information on the president-elect and the transition team and what they were doing,’’ he said.

Nunes’s statements were remarkable on numerous levels. He publicly discussed FISA-approved surveillance, something that Comey had refused to do before Nunes’s committee days earlier. Nunes attributed his information to an anonymous source, after he and other members of his party have bemoaned media reports relying on unnamed people.

Perhaps most significantly, Nunes went to the White House to brief the president on the details of material potentially gathered as part of his panel’s investigation into associates of the president and Russia’s interference in the campaign.

Nunes said that none of what he reviewed involved Trump team contacts with Russian officials. He initially said the collection included details of Trump’s conversations but then backed away from that claim, saying only that it was “possible.”

“I have seen intelligence reports that clearly show that the president-elect and his team were at least monitored and disseminated out in intelligence,’’ he said, adding that he hoped to ascertain who in the government had sought details about the Trump team and had asked for their identities to be revealed, or “unmasked,” in the intelligence reports.

Nunes also said that he hoped to have more information by Friday and had asked the FBI, the CIA and the National Security Agency to “provide a full account of these surveillance activities.”

The directors of the FBI and NSA spent more than five hours Monday being grilled by lawmakers on Nunes’s committee about the counterintelligence probe looking for any evidence of coordination between the Trump campaign and Russian officials during the election. Comey was also asked about Trump’s claims on Twitter that he had been the victim of an Obama-ordered wiretap. “I have no information that supports those tweets,’’ Comey said.

Schiff said that after speaking with Nunes on Wednesday afternoon, the Republican said that most of the names of American citizens were not “unmasked” in the intelligence reports but that it was still possible to ascertain their identities.

“Because the committee has still not been provided the intercepts in the possession of the chairman, it is impossible to evaluate the chairman’s claims. It certainly does not suggest — in any way — that the president was wiretapped by his predecessor,” Schiff said.

Sen. John McCain (R-Ariz.) called Nunes’s actions Wednesday “remarkable” and “bizarre,” and said the partisan jockeying from Nunes and Schiff — with “no substantiation,” McCain added — were turning the House Intelligence Committee’s investigation into a political sideshow.

He called for either a select committee or an independent commission to look into the matter.

“No longer does the Congress have credibility to handle this alone, and I don’t say that lightly,” McCain said on MSNBC.

He stressed, however, that he believes the Senate Intelligence Committee is doing “a good job” with its investigation.

John Wagner, Adam Entous, Abby Phillip, Julie Tate and Ellen Nakashima contributed to this report.