It is hard for Trump to make the case for his own trustworthiness, given his erratic moods, frightening rhetoric and gleeful betrayals. Some in Congress, like Representatives Trey Gowdy and Paul Ryan, have defended the F.B.I.’s Russia investigation and pushed back against the Spygate narrative. “A confidential informant is not a spy,” says Senator Lindsey Graham, undermining Spygate’s central premise. But others want to take seriously the possibility that candidate Trump fell victim to those same imperial powers that Brennan encouraged Obama to use. “There is virtually no abuse of civil liberties that John Brennan hasn’t been a part of,” Senator Rand Paul told me by email, citing drone strikes, torture and surveillance. Later, he called on Brennan to testify publicly about “any secret info on candidate Trump ... from European or British intelligence sources.” Brennan’s warnings about Trump seemed at risk of getting lost in the noise, one among many competing sets of allegations.

“I think his credibility is zero,” Brennan said on MSNBC, hours after the North Korea summit. “He continually lies to the American people and to the public,” he thundered. “How can anybody believe what he is saying?” His jabs were getting sharper and snappier; he was adapting to a media environment in which points don’t land without repetition and hyperbole. He was, in other words, beginning to sound more like his tweets, and perhaps just a bit like Donald Trump.

Brennan’s father, Owen, was a blacksmith who immigrated to New Jersey from Ireland in 1948. Owen’s own father, Brennan told me, was “a supporter, an affiliate, say,” of the Irish Republican Army. Brennan moved twice while growing up, from one apartment to another before settling in a three-family house in North Bergen. His grandmother lived on the top floor. “My dad worked construction in those years,” Tom remembers. “Those jobs were not easy to come by.” When the construction business slowed down, Owen would find odd jobs. For a time, he commuted into Manhattan to fold papers for The Daily News. The Brennans scrimped so John and his brother and sister could be taught by Franciscan nuns, who made heaven and hell as tangible as two neighborhood subway lines. Brennan resolved to go to heaven, and the priesthood seemed like a sure way of getting there. He read about the popes and noticed that there had never been an American one. He decided that he would be the first. “If you’re going to be a priest, why not aspire to be the highest priest there is?” he told me.

As a teenager, even as he absorbed his parents’ morality and work ethic, Brennan felt torn between the cloistered priesthood and a life of worldly experience, between pleasing his parents and escaping into a world that was larger than New Jersey. He read Saint Augustine and Hermann Hesse. He found a mentor in his cousin Thomas, who had traveled to Malaysia and Vietnam and was stationed in Indonesia, working at U.S.A.I.D. Thomas mailed back reel-to-reel audio recordings recounting his travels. On Sundays, after church, the family would gather around the kitchen table at Thomas’s father’s house to listen to them. Thomas told the family how lucky they were to be living in the free world, where there was adequate food and shelter and real opportunity. John wanted to follow Thomas’s example. He applied to and was accepted by the Georgetown School of Foreign Service but could not attend; the tuition was too high. Instead, he enrolled at Fordham, a Catholic university on the other side of the Hudson. He took the bus to school and worked nights at a supermarket deli. He devoted himself to studying Arabic and spent part of his junior year in Cairo.

A few years later, in 1980, as a graduate student in political science at the University of Texas at Austin, Brennan would write his master’s thesis on the state of human rights in Egypt, under the rule of Anwar Sadat. The thesis grapples with a thorny problem of United States policy in the Middle East — how much repression by our allies is tolerable? Brennan responded to the problem with equivocation. In his view, Sadat’s repression of radical groups and censoring of the press was justifiable for the sake of “the preservation of democracy.” Other measures, like interfering with elections, were unjustifiable “regime perpetuation.” In the case of Egypt, he found, the ends do justify the means, but only sometimes.

Back in New Jersey, Brennan married his hometown girlfriend. They had met at a bar in Edgewater; years before, Brennan played Little League baseball with her older brother. As Brennan tells it, he applied to join the C.I.A. around this time, after seeing a newspaper ad. An interviewer strapped his arm to a polygraph machine and asked if he had ever been a member of an organization that sought to overthrow the government of the United States. Brennan, not wanting to carry even the smallest deception on his conscience, said that he voted for Gus Hall, the Communist Party candidate for president, in 1976. (Decades later, Brennan volunteered the story of his Communist vote to a young woman who had asked him if participating in protests might disqualify her from working for the C.I.A. Reports of Brennan’s vote reached right-wing critics of the Obama administration, who tried to use this nearly 40-year-old vote as evidence of ongoing Communist sympathies. Brennan now says that it was cast in protest against the partisanship of the Watergate era.)

At the C.I.A., Brennan quickly distinguished himself as a “deep select,” a young officer given extra visibility and fast promotions. After a tour in Saudi Arabia, he grew close to George Tenet, who was working at the National Security Council as a liaison between the C.I.A. and the Clinton White House, where Brennan sometimes delivered the president’s daily brief. Tenet became Clinton’s third C.I.A. director in 1997, and George W. Bush kept him on. Tenet had repeatedly tried to warn Bush’s team about the growing Qaeda threat, but not everyone shared his sense of urgency. Tenet and Bush took their failure to stop the attacks of Sept. 11, 2001, personally. Waves of guilt and panic poured down through the C.I.A.’s hierarchy as rumors spread that there might be a second wave of attacks. “I remember going into the counterterrorism center,” says Jami Miscik, who led the C.I.A. Directorate of Intelligence at the time. “The analysts had their children sleeping on the floor. It was such an intense effort.”