As one of the longest-serving senior White House officials, and as the National Security Council’s top legal adviser, Eisenberg has been privy to many of the Trump administration’s most sensitive secrets. That makes the 52-year-old lawyer a compelling character in the drama set off by Democrats’ impeachment drive — and, for the president, potentially a dangerous one.

As lawyers often do, Eisenberg took notes in meetings with Trump, a standard practice that “drove the president absolutely bonkers,” according to one former White House official. “His sense was people were taking notes because they were going to write a book or testify against him,” the former official said.

It was Eisenberg to whom several alarmed White House officials turned when Trump urged Ukraine’s President Volodymyr Zelensky to investigate former Vice President Joe Biden and his son Hunter. It was Eisenberg who then helped order the record of that call into a system used for ultra-secret classified information. And it was Eisenberg who, several reports said, consulted with political appointees at the Justice Department on how to handle a whistleblower’s complaint about the Ukraine call.

Friends and colleagues who know Eisenberg also aren’t surprised by his reported actions.

“He keeps confidences. He doesn’t run his mouth about stuff he shouldn’t run his mouth about,” said Michael Mukasey, a former attorney general in the Bush administration who worked with Eisenberg.

“John is a brilliant and careful lawyer,” said Steven Engel, assistant attorney general in charge of the Office of Legal Counsel. “It’s no coincidence that he’s been at the White House through four national security advisers and three White House counsels.”

Others put it differently.

Eisenberg is “extremely paranoid,” in the words of one of his former colleagues at the NSC, where he is responsible for providing legal advice on everything from Syria to national security leak investigations to immigration.

A national security specialist who was previously earning at least $1 million a year as a corporate attorney, Eisenberg is “a classic lawyer,” another former NSC colleague recalled: He never says anything when he can nod his approval and never puts anything in emails if he can say it to your face.

Eisenberg’s conduct is coming under scrutiny in the wake of an explosive report from the intelligence community whistleblower, who alleged that records of Trump’s calls with foreign leaders were being hidden to improperly shield the president. The White House isn’t disputing that memos detailing the president’s conversations have been stored in the system, known as NICE, but officials there insist it was done to protect sensitive calls that could hurt national security from leaking.

News reports, notably a recent account in The Washington Post, have also identified Eisenberg as the White House lawyer contacted by several NSC officials who were alarmed by the president’s July 25 phone call with Zelensky. What Eisenberg did next with that information is a matter of intense interest on Capitol Hill: Democrats have seized on the White House handling of the record of Trump’s Ukraine call to allege a cover-up.

One of those NSC officials, Trump’s former top Russia aide Fiona Hill, told House lawmakers on Monday that she met with Eisenberg twice in mid-July to share her concerns about Rudy Giuliani’s efforts to persuade Ukrainian officials to investigate Joe and Hunter Biden. She did so, Hill said, at the behest of then-national security adviser John Bolton. “I am not part of whatever drug deal Sundland and Mulvaney are cooking up,” Bolton had told her to say, according to a person familiar with Hill’s testimony.

The White House is now reviewing how it handled Trump’s phone call with Zelensky, according to an administration official. Eisenberg is at the center of that review, according to The New York Times, which reported that some aides are worried that the mission of the review is to find a scapegoat.

Some of Eisenberg’s former colleagues are concerned that he will be blamed for the Ukraine scandal, with one of them saying: “The White House is full of political actors with agendas and there can be a lot of knife fights over there. That’s not something that John really engages in.”

If so, it would be a remarkably familiar Washington plot line in a town in the throes of unprecedented political upheaval.

“If I remember D.C.,” observed Mukasey, “it’s a place where a lot of people don’t always carry their weapons in view.”

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Eisenberg, who attended Stanford University as an undergraduate and then studied law at Yale, joined the Trump White House at the start of the administration. He had previously been a partner in the D.C. office of Kirkland & Ellis, a law firm that has been stacked with prominent conservative luminaries over the years, including Supreme Court Justice Brett Kavanaugh, Attorney General Bill Barr and White House Counsel Pat Cipollone.

As the longest-serving deputy in the counsel’s office, Eisenberg is the most prominent remaining link to Don McGahn, Cipollone’s predecessor as the White House’s top lawyer. But unlike his former boss, who provided some of the most damaging testimony in the report by special counsel Robert Mueller and was accused by Trump of leaking, Eisenberg has a legendary reputation for secrecy.

“John was distrustful of information flows to everywhere else in the building,” said a former NSC colleague. “He inherently was of the view that anything that could leak would leak and so he was also incredibly conscious of trying to restrict conversations to only those that he really, really, really felt needed to know.”

Others described Eisenberg as a “by the book guy” whose main concern was protecting the White House from legal risk. He at times raised concerns about actions Trump had proposed, including the extradition of dissident Turkish cleric Fethullah Gülen. On that occasion, a former White House official said, Eisenberg’s objections helped scuttle the idea.

“When John generally found things that he was uncomfortable with or would violate the law, he was often very quick to speak up and say that,” said a former NSC official.

Besides being fearful of leaks, Eisenberg is also anxious about how he appears in the press and is “naturally concerned about how his role is portrayed,” said an administration colleague. “He just doesn’t want to be the center of the story and wants to stay in the background of things. He’s very concerned anytime his name is mentioned” in the press. (Early in the administration, NBC sent a camera crew to Eisenberg’s house to ask him about a secret trip California Rep. Devin Nunes made to the White House to view intelligence on alleged Obama administration wrongdoing.)

Eisenberg has also been the lead lawyer on discussions about finding suspected leakers of national security information in the White House, according to a former White House official and another person familiar with the matter.

Eisenberg would give the legal OK for the White House Communications Agency to look into NSC staffers’ accounts when they were suspected of leaking, according to the former official.

“The attorneys always have to assist in that type of stuff when you’re accessing somebody else’s account. White House counsel always insisted that they participate in any of the fact-finding activities that would go on,” this person said.

One former NSC official said it would make sense if it was Eisenberg who thought of putting the transcripts into the NICE system in the first place. “John is well-meaning but would be the exact type of person who would come up with the idea to stick this into a compartmented system,” the former official said.

“That’s where a lot of confidential stuff goes and has gone and the suggestion that this is somehow subject to special treatment I think is wrong,” Mukasey said, adding that he assumes Eisenberg’s motive would have been to prevent the records from leaking.

Asked whether Eisenberg was being set up as a fall guy, Mukasey said he didn’t know but added: “Washington is a dangerous place, which everybody knows. John is as straight as the edge of your computer screen. He didn’t do anything wrong.”

Making Eisenberg a scapegoat for the Ukraine scandal could prove risky for a president who has alienated many of his former top aides.

As the NSC’s top lawyer, former officials said, Eisenberg likely would have been able to listen in on most calls with foreign heads of state and had a standing invitation to attend every top-level meeting on national security. His portfolio is sprawling, former officials say: He has worked on the Syria airstrikes; U.S. activities in Afghanistan, Iraq and Libya; election security; and the expulsion of Russian diplomats after the poisoning of former Russian spy Sergei Skripal and his daughter in England.

“If there are any buried bodies, Eisenberg knows where they are,” said a former administration official.

“New folks come in and they know that he’s a guy they want to keep on because they can rely on his judgment and his integrity,” said Engel. “John is a careful lawyer of high integrity, and based on my past work with him, I have every reason to think that he would deal with the situation appropriately as it arises.”

Eisenberg’s ties to the traditional GOP establishment distinguish him from many of the officials who joined the Trump administration in the wake of his surprise victory in 2016. He donated the maximum $2,700 to Jeb Bush’s primary campaign in August 2015, but unlike many of his former Bush colleagues, he did not sign any of the “Never Trump” letters circulating during the campaign.

Before joining Kirkland & Ellis, he spent a year as associate deputy attorney general in the George W. Bush administration, where he worked on national security matters. Eisenberg’s name is one of several on a 2008 top secret DOJ brief to a court arguing the government’s position in favor of one of the Bush administration’s controversial surveillance programs, along with John Demers, the current head of the national security division at the Department of Justice.

Mukasey recalled his worry at the time that Keith Alexander, who was then director of the National Security Agency, “essentially wanted to kidnap” Eisenberg to bring him over to work at Fort Meade. “He wanted him in the worst way, and it was because of his intelligence and insight,” Mukasey said.

Eisenberg is “closer to what you imagine would be the sorts of people who would be filling those roles in a more traditional Republican administration,” said one former official. “He’s not somebody who you would think of as the crazy Trump Train.”

Still, another former administration official noted that, amid internal discussions on hot-button immigration issues in 2018, Eisenberg told colleagues to hew closely to Trump’s wishes on the issue. “No, no, no: This is the president’s objective,” this person paraphrased him saying. “This is where we need to go.”

Nancy Cook contributed to this report.