Henry Kissinger and Daniel Ellsberg did their undergraduate and graduate studies at Harvard around the same time, both young veterans on scholarship and both brilliant and precocious. And it was Ellsberg, stationed in the US embassy in Saigon, who briefed Kissinger during his first visit to South Vietnam.

Like Kissinger, Ellsberg was interested in the question of contingency and choice in human affairs. But Ellsberg approached the subject as an economist, going on to do groundbreaking work in game theory and abstract modeling. Focused on atomized individuals engaged in a series of rational cost-benefit transactions aimed to maximize their advantage, these methods were far removed from Kissinger’s metaphysical approach to history, ideas, and culture.

Kissinger, in fact, had Ellsberg’s kind of methodology in mind when he criticized, in his undergraduate thesis, the smallness of American social science and the conceits of “positivism,” the idea that truth or wisdom could be derived from logical postulates or mathematical formulas.

Ellsberg spoke the language of axioms, theorems, and proofs, and believed that sentences like this could help defense strategists plan for nuclear war:

For any given probability distribution, the probability of outcome a with action III is p(A ∪ C) = P_A + P_C. The probability of outcome a with action IV is p (B ∪ C) = P_B + P_C. . . . . This means there must be a probability distribution, P_A P_B P_C (0 ≤ p_i ≤ p ∑ p_i = 1), such that P_A > P_B and P_A + P_C < P_{B +} P_C. But there is none.

In contrast, Kissinger the metaphysician, wrote things like:

It does not suffice to show logically deduced theorems, as an absolute test of validity. There must also exist a relation to the pervasiveness of an inward experience which transcends phenomenal reality. For though man is a thinking being, it does not follow that his being exhausts itself in thinking. . . . the microcosm contains tension and polarity, the loneliness of the individual in a world of strange significances, in which the total inner meaning of others remains an eternal riddle. Rhythm and tension, longing and fear, characterize the relationship of the microcosm to the macrocosm.

The clash between these two ways of thinking about human experience would play themselves out in the first few months of Kissinger’s tenure as Nixon’s national security adviser.

Shortly before Nixon’s inauguration, Ellsberg, in a meeting with Kissinger at the president-elect’s headquarters at the Pierre Hotel in Manhattan, offered some advice. He related a story of how Robert McNamara, soon after being named secretary of defense, shook up the bureaucracy by immediately flooding Pentagon officers and staff with written questions. The answers he received weren’t important. McNamara was merely establishing his dominance.

Ellsberg suggested Kissinger do something similar: draft questions on controversial issues and send them out to the whole bureaucracy, to every agency and office. The agency principally responsible for any given subject, Ellsberg predicted, would have one opinion on the matter, and secondary agencies would have another, and the difference between the two opinions would provide a useful map of the ambiguities, doubts, and uncertainties that existed in the bureaucracy.

But, Ellsberg said, there was another, more Machiavellian reason to conduct the survey. The “very revelation of controversies and the extremely unconvincing positions of some of the primary agencies,” he said, “would be embarrassing to the bureaucracy as a whole. It would put the bureaucrats off-balance and on the defensive relative to the source of the questions — that is, Kissinger.”

“Kissinger,” Ellsberg remembered, “liked the sound of that.”

The questions, as Ellsberg predicted, prompted a backlash. Soon a counterproposal for reorganizing the NSC around the State Department began to float around, which allowed Kissinger to identify potential rivals. The proposal was quashed and its authors were sidelined.

That first stage of the exercise worked well for Kissinger. The next, not so much.

Kissinger had asked Ellsberg to collate, analyze, and average the responses to the questions related to the Vietnam War, over five hundred pages in total. The gloom revealed by the survey was astounding.

Even those hawks “optimistic” about the pacification of Vietnam thought that it would take, on average, 8.3 years to achieve success. All respondents agreed that the “enemy’s manpower pool and infiltration capabilities can outlast allied attrition efforts indefinitely” and that nothing short of perpetual troops and bombing could save South Vietnam.

When the findings were presented to Kissinger, he must have immediately recognized the trap he had fallen into. For all his warnings about how the “accumulation of facts” by technocrats like Ellsberg has the effect of sapping political will, Kissinger had foolishly given him free rein to, in effect, data mine the bureaucracy, providing him with hard evidence that the majority of the foreign service thought the war either was unwinnable or could be won only with actions that were politically impossible: permanent occupation or total obliteration.

Kissinger was the statesman, Ellsberg the expert. And according to Kissinger’s worldview, Ellsberg shouldn’t have existed, or at least he shouldn’t have done what he did.

Ellsberg was what Kissinger in his undergraduate thesis called a “fact-man.” His faith in data, his belief that he could capture the vagaries of human behavior in mathematical codes and then use those codes to make decisions, should have led him to a state of, if not paralysis, then predictability.

Kissinger would later boast about the difference between statesmen and experts, writing “the scope of the statesman’s conception challenges the inclination of the expert toward minimum risk.” But it was Ellsberg who was speaking out against the war and then leaking top-secret documents, taking a tremendous risk, including the possibility of imprisonment. And with this one audacious act, he changed the course of history.

The difference between Ellsberg and Kissinger is illustrated by the Pentagon Papers themselves. The “major lesson” offered by the massive study, Ellsberg thought, “was that each person repeated the same patterns in decision making and pretty much the same policy as his predecessor without even knowing it,” thinking that “history had started with his administration, and had nothing to learn from earlier ones.” Ellsberg, the economist, believed that breaking down history into discrete pieces and studying the decision making process, including the consequences of those decisions, provided a chance to break the destructive pattern.

But when Ellsberg tried, in their last meeting before leaking the documents, to get Kissinger to read the papers, Kissinger brushed him off.

“Do we really have anything to learn from this study?” he asked Ellsberg, wearily. “My heart sank,” recalls Ellsberg.

On Monday, June 14, 1971, the day after the New York Times published its first story on the papers, Kissinger exploded. He waved his arms, stomped his feet, and pounded his hands on a Chippendale table, shouting: “This will totally destroy American credibility forever. . . . It will destroy our ability to conduct foreign policy in confidence. . . . No foreign government will ever trust us again.”

The Pentagon Papers were a bureaucratic history of America’s involvement in Southeast Asia up until Johnson’s presidency. There was nothing specifically damaging to Nixon. But it was Kissinger’s “fury” that convinced Nixon to take the matter seriously. “Without Henry’s stimulus,” John Ehrlichman said, “the president and the rest of us might have concluded that the Papers were Lyndon Johnson’s problem, not ours.”

Why? The leak was bad for Kissinger in a number of ways. He was just then negotiating with China to reestablish relations and was afraid the scandal might sabotage those talks. He feared that Ellsberg, working with other dissenters on the NSC staff, might have breached the closed informational circuit that he had worked hard to establish, perhaps even acquiring classified memos on Cambodia.

Also, on a more abstract level, the Pentagon Papers really were something conjured out of Kissinger’s worst anti-bureaucratic fever dream. The project was a huge endeavor, written by an anonymous committee staffed by scores of what Robert McNamara called “knowledgeable people” drawn from the mid-level defense bureaucracy, universities, and social science think tanks.

Headed by two “experts,” Morton Halperin and Leslie Gelb, the committee based its findings on the massive amount of paperwork produced by various departments and agencies over the years — what Kissinger in his undergraduate thesis dismissed as the “surface data” of history. Missing, therefore, from its conclusions was what the young Kissinger would have described as the immanent possibility, the contingency, the intuition, and “freedom” that went into every decision point.

But Kissinger’s rage was also as much about the leaker as about the leak, obvious in the way he swung between awe and agitation when describing Ellsberg to his coconspirators, as almost Promethean in his intellect and appetites. “Curse that son of a bitch, I know him well,” he began one Oval Office meeting.

Kissinger keyed his performance to stir up Nixon’s varied resentments, depicting Ellsberg as some kind of liberal and hedonistic superman — smart, subversive, promiscuous, perverse, and privileged: “He’s now married a very rich girl,” Kissinger told Nixon. “Nixon was fascinated,” Ehrlichman said. “Henry got Nixon cranked up,” Haldeman remembered, “and then they started cranking each other up until they both were in a frenzy.” “Kissinger,” he said, “was absolutely infuriated and, in his inimitable fashion, managed to beat the president into an equal froth of fury.” Alexander Haig said that Kissinger, “did drive the president’s concern” about the leak.

It was in the meeting where Kissinger gave his most detailed denunciation of Ellsberg that Nixon ordered a series of illegal covert operations, putting Nixon on the road to ruin. These included the break-in at the Democratic National Committee headquarters at the Watergate Hotel and the burglary of Ellsberg’s psychiatrist’s office in California, hoping to find information that could be used to “discredit his character.”

“He’s nuts, isn’t he?” Haldeman asked Kissinger, about Ellsberg, in one of their meetings.

“He’s nuts,” Kissinger answered.

For what must have been for him a long year, between mid-1973 and mid-1974, it seemed Henry Kissinger, now holding the position of both national security adviser and secretary of state, was going down with Richard Nixon, along with his top aides.

Kissinger almost got caught on Cambodia, when Maj. Hal Knight sent a whistle-blowing letter to Senator William Proxmire informing him of his falsification of records. The Senate Armed Services Committee held hearings through the middle of 1973, and Seymour Hersh came very close to establishing Kissinger’s involvement in setting up the dual record reporting system. Hersh couldn’t confirm Kissinger’s role (he would at a later date) but that didn’t let Kissinger off the hook.

In June 1974, Hersh widened the net, filing stories fingering Kissinger for the first round of illegal wiretaps the White House set up, done in the spring of 1969 to keep the Cambodia bombing secret. Reporters, senators, and representatives were circling, asking questions, digging up more information, issuing subpoenas.

Landing in Austria, en route to the Middle East, and finding that the press had run more unflattering stories and editorials, Kissinger took a gamble. He held an impromptu press conference and threatened to resign (this was June 11, less than two months before Nixon’s resignation). It was by all accounts a bravura turn. “When the record is written,” he said, seemingly on the verge of tears, “one may remember that perhaps some lives were saved and perhaps some mothers can rest more at ease, but I leave that to history. What I will not leave to history is a discussion of my public honor.”

The bet worked. The press gushed. He “seemed totally authentic,” New York Magazine wrote. As if in recoil from the unexpected assertiveness they had shown in recent years, reporters and news anchors rallied around. The rest of the White House was being revealed to be little more than a bunch of shady two-bit thugs, but Kissinger was someone America could believe in.

“We were half-convinced,” Ted Koppel said in a documentary in 1974, just after Kissinger’s threatened resignation, “that nothing was beyond the capacity of this remarkable man.” The secretary of state was a “legend, the most admired man in America, the magician, the miracle worker.”

Kissinger, Koppel said, “may be the best thing we’ve got going for us.”

Kissinger’s Shadow: The Long Reach of America’s Most Controversial Statesman is out now from Metropolitan Books.