President Ronald Reagan, ever the optimist, was distraught. He was pacing the living room at the U.S. ambassador’s residence in Reykjavik, Iceland, on Sunday, Oct. 12, 1986, just minutes after failing to reach an agreement with Soviet leader Mikhail Gorbachev. James Kuhn, the president’s aide, recalled that he had never seen Reagan look this way. The president was standing alone, his face forlorn.

Reagan later described the Reykjavik summit as a great success, and in some important ways it was. But in those first hours after it ended, Reagan seemed to have let slip from his grasp a chance to end the nuclear arms race. Everyone was grim. The failure seemed large.

The summit was one of the most dramatic and spontaneous moments of the Cold War, and historians, memoirists, archivists and playwrights have since returned to the scene, peering through the curtains of Hofdi House in hopes of gaining a better understanding of how Reagan and Gorbachev came so close to eliminating nuclear weapons and then walked away. The allure of the story has been deepened in recent years by the release of official notes taken by each side.

Ken Adelman tackles this history with his views well established and on full display. This book is a paean to Reagan. “A mere blink of history after Reagan stood tall at Reykjavik,” Adelman writes, “the Soviet Union came down, thereby ending decades of danger. My contention is that these events were not merely coincidental.” At Reykjavik, he says of Reagan, “we see a man with surprising depth and dexterity on the critical issues of his day.” According to Adelman: “The Cold War thus ended just as Ronald Reagan had said it would. We won. They lost.” Describing a moment when Reagan appears in Reykjavik to talk with his staff, Adelman says: “I always felt awed to be in the presence of the president. . . . I felt a tingle in the back of my neck.”

Adelman, who was at the summit as director of the U.S. Arms Control and Disarmament Agency, recounts the weekend’s roller coaster of expectations and emotions. Reagan went to the summit clueless about what to expect. Gorbachev came prepared with tempting and detailed concessions on reducing strategic and intermediate-range nuclear weapons. Reagan jumped at the offers, having long harbored an aspiration to abolish nuclear weapons. At a key moment on the second day, he let loose with words that had never been spoken at such a summit, proposing to eliminate all nuclear weapons. Gorbachev said yes. “Then let’s do it,” declared Secretary of State George Shultz. But later that day, Gorbachev sprang a trap, saying all his proposals were a package deal and the package included a limit on research for Reagan’s cherished Strategic Defense Initiative (SDI), a proposed missile defense system that was just at the early research phase. Gorbachev wanted to restrict testing to the laboratory for a decade. Reagan refused, and they had no deal. It fell apart over one word, “laboratory.” But the summit paved the way for later arms-control agreements.

The front cover to "Reagan at Reykjavik: Forty-Eight Hours That Ended the Cold War" by Ken Adelman. (HarperCollins Publishers/HarperCollins Publishers)

Adelman does not add much new, but his account, written in a breezy manner, contains interesting nuggets. He admits that Reagan’s repeated offer to share SDI with the Soviets was “splendidly naive” and “rather silly.” He also suggests that the U.S. Pershing II intermediate-range missile, deployed in Europe in 1983, was a “lemon.”

During the summit, Adelman wasn’t in the room with Reagan and Gorbachev, but upstairs with the U.S. and Soviet delegations, and he took part in the long, overnight, expert-level negotiations. He depicts confusion and uncertainty. Were they talking about eliminating ballistic missiles, or offensive missiles, or nuclear missiles? Reagan spoke interchangeably about all three. Gorbachev used “nuclear forces” and “offensive weapons” without distinction. Reykjavik was history being not only made, but improvised.

The weakness of Adelman’s account is that he doesn’t do justice to Gorbachev’s radical ambitions. This was a blind spot back in Reagan’s day, too. Soviet disarmament campaigns were considered just another blast of propaganda. “We in the Reagan administration remained skeptical,” Adelman writes, “never for a minute imagining that this time this Russian leader might actually be serious about seeking fewer weapons.”

But Gorbachev was serious. In January 1986, he called for eliminating all nuclear weapons by the year 2000. When Shultz went to tell Reagan about the news from Moscow, Reagan replied, “Why wait until the end of the century for a world without nuclear weapons?” In April and May, the Chernobyl nuclear accident further deepened Gorbachev’s resolve. He had already faced down demands from his military-industrial complex to build a vast new Soviet missile defense system. He had put a moratorium on nuclear testing. He told aides preparing for the summit that his goal was “liquidation of nuclear weapons.” By the time he got to Reykjavik, Gorbachev was hell-bent on dramatic results. But by Adelman’s account, Gorbachev “merely wanted the standard-fare Nixon-Ford-Carter arms control to move along faster.” A better assessment is that of James Graham Wilson in “The Triumph of Improvisation,” published in February by Cornell University Press; he concludes that Gorbachev was “the indispensible agent of change.”

Reagan clung fiercely to SDI at Reykjavik, even though it was no more than a gauzy dream at that point. Adelman observes correctly, “Reagan wanted so badly to build it and Gorbachev wanted so badly to stop it, that it assumed for them, and practically only for them, a reality it actually lacked.”

But Adelman then resurrects the unpersuasive argument that SDI led the Soviet Union to collapse. “SDI became the straw that broke the Communist camel’s back,” he claims. This is an old chestnut that gives Reagan too much credit. The threat of SDI and superior American technology certainly worried the Kremlin. But the Soviet Union collapsed because of profound internal weaknesses — fault lines that were systemic and that Gorbachev widened in his valiant efforts at reform. That narrative does not console those who want to put Reagan on an ever-higher pedestal, but it is closer to the truth.

David E. Hoffman is a contributing editor to The Washington Post and the author of “The Dead Hand: The Untold Story of the Cold War Arms Race and Its Dangerous Legacy,” which won the Pulitzer Prize for general nonfiction in 2010.