This year marks the sixtieth anniversary of high-altitude summitry—both diplomatic and Himalayan—and it finds us at a moment of immense possibility and risk: when Presidents Obama and Xi Jinping meet in the California desert tomorrow, away from the hothouses of Beijing and Washington, the unusual circumstances will reflect an attempt to short-circuit the feeling, on both sides, that a dangerous energy is accumulating in the diplomatic relationship of the world’s two most important countries. The format has produced both successes and failures. The historian David Reynolds, the author of “Summits: Six Meetings That Shaped the Twentieth Century,” told me this week that “personal summits”—those aimed at establishing mutual understanding more than deal-making—are “high risk.” They can change history—or they can “go badly wrong if chemistry doesn’t work,” he said.

By history’s standards, this week’s setting has its advantages. When Churchill, Roosevelt, and Stalin convened in February, 1945, they resigned themselves to war-ravaged Yalta, on the banks of the Black Sea, only because Stalin refused to travel abroad. The airstrip was a cow pasture, the port was loaded with German mines, and the palaces where the attendees stayed had been looted of everything, including the beds and plumbing. “If we had spent ten years on research, we could not have come up with a worse place in the world,” Churchill remarked, and demanded abundant whiskey to survive the experience. By contrast, the Sunnylands estate, in Rancho Mirage, which once belonged to the publishing magnate Walter Annenberg, exudes the kind of khaki-and-club-soda ethos of the generation descending on it. Xi does not golf, sources close to the matter report, so the principals will be photographed on a constitutional through the palmetto scrub.

The White House is talking down the prospects of a major announcement. Instead, they are looking for rapport. They have planned six hours of informal talks on a list of topics including cyber security, North Korea, human rights, and military relations. Among other things, the White House will be looking for signs that Xi, more than his predecessors, recognizes that China’s cyber-espionage campaign, especially against corporations, is now perceived as a strategic threat, not simply a cost of doing business. Likewise, “President Obama must be willing to more directly signal U.S. acknowledgment of China’s arrival as a great power and with that, a role in shaping new global rules and norms,” the former C.I.A. analyst Christopher Johnson wrote this week.

The open-ended agenda has its perils, however. In 1961, newly elected John F. Kennedy proposed an informal meeting with Soviet Premier Nikita Khrushchev, and they met for a two-day summit in Vienna. It was toxic; the two men clashed over the status of Berlin, nuclear weapons, and wars of national liberation, and, at the end, Khrushchev said, “It is up to the U.S. to decide whether there will be war or peace.” Kennedy responded, “Then, Mr. Chairman, there will be war. It will be a cold winter.”

By contrast, I think the chances of success this week are high. U.S.-China summits have gone best when they’ve been about building a relationship rather than trading protocol. Mao was able to have Nixon to Beijing in 1972 because he had the authority to defy critical voices in his own Party; in 1979, Deng Xiaoping could tour the U.S., ham it up with the Harlem Globetrotters, and wear a cowboy hat because he had consolidated power at home. But in 2011, the pallid President Hu Jintao needed every bit of his twenty-one-gun salute to appear Presidential—and was able to do little more than recite collective talking points. By agreeing to a casual meeting, Xi Jinping has shown that, less than a year into office, he has organized enough backing to allow him to go off-script earlier than expected.

The comparison to Kennedy and Khrushchev can sound melodramatic; the stakes this time are lower in the short term. But they are just as high in the long term. I am optimistic about the chances for success. Both sides know they cannot afford to insult or bully—and neither man is known for it. More importantly, they know that history has been unkind to great powers who fail to come to an accommodation. Neither side wants conflict, but, as of today, neither can exclude the possibility. That is a powerful motivator. “The ultimate question,” Reynolds wrote, “is whether a leader feels that in the last resort he can afford to walk away empty-handed.” The summit in the desert will be the rare case in which neither side can afford to leave empty-handed—or to run the table.

Above (left to right): Winston Churchill, Franklin Delano Roosevelt, and Joseph Stalin, during the Three Power Conference at Yalta, in 1945. Photograph: Herbert/Hulton Archive/Getty.