Though Mr. Obama was 8,500 miles from Washington, he could not quite let go of election-year politics. At one point, he noted that many societies, particularly in the Arab world, fracture along tribal lines, and that the great virtue of the United States was its openness to people from all races, creeds and nationalities. “Not everybody in America agrees with me on this, by the way,” Mr. Obama said, apparently teeing up an unfavorable reference to the Republican presidential nominee, Donald J. Trump. After a pregnant pause, the president smiled and said, “I’ll leave it at that.”

Mr. Obama expressed no misgivings about putting so much emphasis on Southeast Asia. “If we weren’t here, interacting and learning from you, and understanding the culture of the region, we’ll be left behind,” he said. “We’ll miss an opportunity.”

Mr. Obama has begun talking about what he will do after his presidency. One project is to continue his involvement with the Young Southeast Asian Leaders Initiative, and he said his presidential center would work with the group. His wife, Michelle, plans to travel more abroad to work on global health issues, he said.

The president flew to Laos to attend a pair of regional conferences: the Association of Southeast Asian Nations meeting and the East Asia Summit meeting. He has a near-perfect attendance record at these meetings; George W. Bush and his secretary of state, Condoleezza Rice, were regularly no-shows. The Obama administration’s cultivation of ties with Southeast Asia sets it apart from previous administrations, which have tended to place China at the fulcrum of their Asia policies.

While much of the president’s trip was devoted to the future, he spent time in Laos confronting America’s wartime past: a secret bombing campaign from 1964 to 1973 that left 80 million cluster bombs buried in rice paddies and forests, where farmers and children step on them and are killed or maimed (the State Department recently issued a warning for people playing the game Pokémon Go to watch out for land mines).

In Vientiane, the capital, Mr. Obama toured an American-funded center that searches for explosives in the countryside and that provides prosthetic legs and rehabilitation services to victims of ones that have gone off. “For the people of Laos, the war did not end when the bombs stopped falling,” Mr. Obama said, a display of prosthetic legs behind him. “They were spread across farmlands, jungles, villages, rivers. So for the last four decades, Laotians have continued to live under the shadow of war.”