Jonathan Ernst / Reuters

Embattled House Intelligence Committee chairman Devin Nunes is now facing Democratic calls for his recusal from an investigation into the Trump administration’s ties to Russia, as the inquiry grinds to what is at least a temporary halt.

The California Republican has been on the hot seat since announcing last week that he had vague but significant information about “incidental collection” of information about Trump transition team members by U.S. intelligence agencies. “Incidental collection” is when the communications of someone who is not the target of surveillance are picked up because they are corresponding with a target.

But the revelation, and moreover the manner in which he made it and has conducted himself since, has drawn sharp criticism, including from members of his own committee.

Monday night, Representative Adam Schiff, the ranking Democrat on the committee, called for Nunes to step down from the investigation into, among other things, whether members of the Trump team colluded with Russia to interfere in the presidential election, as well as any look into incidental collection of Trump team members.

“This is not a recommendation I make lightly, as the chairman and I have worked together well for several years,” Schiff said in a statement. “But in much the same way that the attorney general was forced to recuse himself from the Russia investigation after failing to inform the Senate of his meetings with Russian officials, I believe the public cannot have the necessary confidence that matters involving the president’s campaign or transition team can be objectively investigated or overseen by the chairman.”

Shortly after Schiff’s statement, House Minority Leader Nancy Pelosi echoed his call for Nunes to recuse himself.

But Nunes rejected the calls, saying, “Why would I?”

Nunes’s role has always been an uneasy one. He himself was a member of the Trump transition team’s Executive Committee, and Schiff and other critics have said he must choose between acting as a White House surrogate and acting as independent overseer. Nunes’s own actions and statements, including briefing the president before even informing other committee members about his revelation Wednesday, and his statement to Sean Hannity that he felt the need to inform Trump because the president was taking press criticism, have heightened the tension.

One problem with removing Nunes from the equation is that he obtained the revelations, such as they are, himself from a source, and it’s unclear who else has seen them. On Monday, after CNN broke the news that Nunes had visited the White House complex to view the information prior to his Wednesday announcement, he told Bloomberg View’s Eli Lake that his source was an intelligence official. Nunes has also said that no one in the administration knew about his visit. That claim has been the subject of skepticism from critics, including former Obama officials, who say no one could have visited the White House grounds, let alone used its secure facility for viewing intelligence material, without being cleared by White House staff.

Speculation has begun to focus on Michael Ellis, who was general counsel for the House Intelligence Committee until he was hired as special assistant to the president, senior associate counsel to the president, and deputy national security council legal adviser. Notably, Ellis is also an intelligence officer in the Navy Reserve—though if he was the source, it would contradict Nunes’s claims that no administration official was aware of his visit and that the White House did not know of the incidental collection before he briefed Trump.

Michael Isikoff reports that panel staffers believe Ellis may be the source. “A White House official and spokesman for Nunes declined to comment on whether Ellis was involved in providing information to Nunes, as did a spokesman for Schiff,” Isikoff added. “White House press secretary Sean Spicer insisted that White House officials were not aware of Nunes’ secret trip to meet his source and referred all questions to Nunes’ office.”

Democrats alone have little power to force Nunes to step down, as they are in the minority. All they can do is raise a fuss and try to attract press attention that might put pressure on the chairman. That also creates an opening for other critics especially on the Senate side. John McCain has previously called for an independent commission to investigate Russian interference, and Tuesday morning the Arizona Republican said on CBS News that Nunes should reveal his source.

In the meantime, however, the acrimony seems to have brought the investigation to a halt. On Friday, Nunes suddenly announced he was canceling a hearing scheduled for Tuesday with former top Obama administration officials, one of many steps that angered Schiff.

Former Acting Attorney General Sally Yates, an Obama holdover fired by the Trump administration for saying the Justice Department would not defend the president’s Muslim travel ban, was one of the witnesses scheduled to testify. The Washington Post reports now that the White House sought to block Yates’s testimony on grounds of executive privilege. Yates’s lawyer argued Friday she was not covered and said she intended to appear. That day, Nunes announced he was canceling the hearing. Now all meetings this week have been canceled because of the partisan battle.

Aside from the question of why Nunes has conducted himself in a strange cloak-and-dagger fashion, and of whether he is acting as a Trump ally or an investigator, there remain many questions about what, exactly, he revealed. Nunes said that Trump transition team officials were caught up in surveillance of foreign targets, and that as far as he could tell, all the surveillance was lawful. It’s neither unusual or unlawful for this to happen, but the names of U.S. persons are supposed to be “masked,” or redacted.

Nunes has complained that there was insufficient masking and that reports featuring identifiable people were too widely circulated within the Obama administration during its closing days. While it initially appeared that Trump transition officials were directly caught in the surveillance, Nunes has since softened that claim, so that it’s possible Trump aides’ communications were not collected at all and were merely discussed by those under surveillance—and it’s not especially surprising that foreign officials would discuss figures in an incoming administration.

Nunes finds himself in a difficult bind. The questions of what masking and circulation are appropriate carry some subjectivity, and in order to substantiate his accusation that intelligence material was too widely shared with insufficient masking, Nunes is forced to ever more widely share the relevant intelligence material.

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