After his reelection in 1984, President Ronald Reagan sat for an interview with Time magazine. “I just happen to believe that we cannot go into another generation with the world living under the threat of those weapons and knowing that some madman can push the button some place,” he said. “My hope has been, and my dream, that we can get the Soviet Union to join us in starting verifiable reductions of the weapons. Once you start down that road, they’ve got to see how much better off we would both be if we got rid of them entirely.” In his dealing with the Soviets, Reagan’s two terms were almost those of two different presidents. Both the hard-liner and the peacemaker were present throughout, but the balance shifted so decisively from one to the other as to create a discontinuity. The man who had denounced the nuclear freeze as Soviet propaganda was now suggesting not just reduction but elimination of all nuclear weapons.

What explains Reagan’s remarkable transformation from Cold War hawk to nuclear peacemaker? His nuclear abolitionism had deep roots, going back to a flirtation with pacifism in the early 1930s. His antiwar side was connected to narratives and images that deeply affected him: seeing the British antiwar play Journey’s End in 1929, being shown footage from the liberation of Auschwitz in 1945, and watching the ABC television movie The Day After in 1983. A projection that stuck with him was that at least 150 million Americans—two-thirds of the population in 1980—would be killed in an all-out nuclear war, though he believed for some reason that Soviet losses would be limited to a much smaller percentage. Advisers who “tossed around macabre jargon about ‘throw weights’ and ‘kill ratios’ as if they were talking about baseball scores” appalled him. In his diary and to aides, Reagan even worried that the biblical prophecy of Armageddon was at hand.

With the elevation of Mikhail Gorbachev as the new Soviet leader in March 1985, Reagan’s hopes for a nuclear peace rose. The 54-year-old Gorbachev was well educated and had traveled extensively in the West. He understood English, he wasn’t dying (like his elderly predecessors Leonid Brezhnev, Yuri Andropov, and Konstantin Chernenko), and he even appeared to have a sense of humor. His wife, Raisa, was often at his side, like an American first lady. In his initial months in power, Gorbachev announced a unilateral freeze on deploying intermediate-range missiles in Europe and began speaking in public about the need for perestroika, economic reform. Former Secretary of State Henry Kissinger, former President Richard Nixon, and others gave Reagan their opinion that Gorbachev represented no change at all. But British Prime Minister Margaret Thatcher disagreed. “I like Mr. Gorbachev. We can do business together,” she told the BBC after meeting him for the first time. Thatcher bolstered Reagan’s optimism about the Soviet leader when she visited him at Camp David and delivered a more detailed assessment, warning him, however, that “the more charming the adversary, the more dangerous.”

Gorbachev’s situation paralleled Reagan’s in several ways. He, too, wanted to serve as an agent of societal and political transformation, taking on the alcoholism rampant in Soviet society as well as its faltering economy. Like Reagan, he relied on his own experience more than on the bureaucratic apparatus beneath him. He shared Reagan’s aversion to the logic of mutually assured destruction. Around the same time that Reagan told Soviet foreign minister Andrei Gromyko he wanted to eliminate nuclear weapons, Gorbachev said the same thing in a speech in London. And where Reagan had Secretary of State George Shultz to encourage his evolution, Gorbachev had Eduard Shevardnadze, whom he selected to replace Gromyko as foreign minister.

The chief obstacle to the relationship Reagan wanted with the new Soviet leader was Reagan’s cherished fantasy of a space-based missile-defense program, the Strategic Defense Initiative. In the run-up to their summit meeting in Geneva in November 1985, the first meeting of American and Soviet leaders in six years, Gorbachev sent Reagan a letter proposing a 50 percent cut in intercontinental ballistic missiles, contingent on a complete ban on space weapons. In negotiating sessions, Gorbachev went even further: If the United States gave up the militarization of space, he would be willing to reduce all nuclear forces to zero. Shultz now realized how frightened the Soviets were of SDI, which depended on technology they didn’t know how to develop and couldn’t afford, and he saw missile defense as a crucial bargaining chip to trade for Soviet concessions.

What Shultz did not yet realize was that Reagan would under no circumstances give up the space initiative. Although missile defense had yet to be successfully invented, Reagan viewed SDI as the key to realizing his dream of eliminating nuclear weapons. “We believe that it is important to explore the technical feasibility of defensive systems which might ultimately give all of us the means to protect our people more safely than do those we have at present, and to provide the means of moving to the total abolition of nuclear weapons, an objective on which we are agreed,” he wrote to Gorbachev on April 30, 1985. “I must ask you, how are we ever practically to achieve that noble aim if nations have no defense against the uncertainty that all nuclear weapons might not have been removed from world arsenals? Life provides no guarantee against some future madman getting his hands on nuclear weapons.”

Over the next year, a remarkable transformation took place as Gorbachev and Reagan became jointly enraptured with the idea of ending the balance of terror, and they pursued that end over near-universal objection inside their own governments. In January 1986, Gorbachev wrote Reagan with a proposal: eliminate all nuclear weapons by 2000. “Why wait until the year 2000?” Reagan responded to aides in the Oval Office. Secretary of Defense Caspar Weinberger and CIA Director William Casey, who had done their best to sabotage earlier nuclear treaties, were appalled. Few others inside the Reagan administration took the idea of nuclear abolition seriously. But Shultz did. He ordered the State Department’s arms-control group to get to work on the question of “what a world without nuclear weapons would mean to us” and how to get there. “I know that many of you and others around here oppose the objective of eliminating nuclear weapons, but the president of the United States doesn’t agree with you, and he has said so on several very public occasions,” he told his colleagues. After much back-and-forth, Weinberger and Shultz were able to agree on a proposal to eliminate ballistic missiles, which Reagan sent to Gorbachev in July 1986.

Gorbachev’s anti-nuclear feelings only intensified after the calamitous accident at the Chernobyl nuclear reactor in April 1986, which left the Soviet leader all the more eager for an agreement. So, too, did the Soviet Union’s deteriorating economic situation. In the fall of 1985, Saudi Arabia announced plans to increase oil production. By the spring of 1986, the world price of oil plummeted from more than $30 a barrel to less than $10. Without hard-currency oil revenue, there was no way for the Soviets to pay for imports of grain and other basic commodities while servicing their foreign debt and keeping up militarily. “The United States has an interest in keeping the negotiations machine running idle, while the arms race overburdens our economy,” Gorbachev told a colleague. “That is why we need a breakthrough; we need the process to start moving.” In September 1986, Gorbachev wrote Reagan offering a number of unilateral concessions and proposing a meeting ahead of his planned visit to the United States the following year. Shultz encouraged Reagan to meet Gorbachev in Reykjavik, Iceland, the following month.

Gorbachev arrived at Reykjavik intending to put a significant disarmament package on the table, contingent on Reagan’s agreement to slow down the development of space weapons. In fact, Gorbachev’s proposal was essentially the one he had originally proposed in the run-up to the Geneva summit: a 50 percent cut in the ICBMs that were the core of the Soviet nuclear arsenal and the total elimination of intermediate-range missiles in Europe. But now Gorbachev was willing to treat limited research on space-based missile defense as compatible with the Anti-Ballistic Missile Treaty. The United States had only to agree to confine its SDI research to the laboratory for ten years and commit not to withdraw from the ABM Treaty for five years after that.

Over dinner with his advisers, Reagan returned to the even more sweeping idea that he’d raised previously: why not the complete elimination of ballistic missiles? The next day, with Gorbachev, the sky was the limit. When the Americans laid all their ICBMs on the table, Gorbachev called and raised by proposing the elimination of all strategic nuclear weapons, including submarines and bombers, over ten years. His bid was still contingent on ten years of adherence to his narrow interpretation of the ABM Treaty and its limits on missile defense, but he indicated he’d be willing to negotiate on that point. This seemingly minor disagreement about how long SDI research would stay confined to the laboratory blocked what would have been the most sweeping arms-control agreement in history. Knowing his own bottom line and grasping Gorbachev’s, Reagan realized that they could go no further. The meeting, so close to a momentous transformation, ended when the president got up and walked out with Shultz while Gorbachev was still decrying the destabilizing effects of SDI.

“This meeting is over,” he said. “Let’s go, George.”

“Can’t we do something about this?” Gorbachev pleaded.

“It’s too late,” Reagan replied.

This article has been adapted from Jacob Weisberg’s forthcoming book, Ronald Reagan.