WITH THE U.S. threatening to increase the pace of its withdrawal from Afghanistan, and Iraq sinking deeper into violence now that the Americans are gone, a lot of people make facile analogies to Vietnam. But a lot of those people weren’t alive in 1975, when that thankless war drew to an ignominious end. Frank Snepp was right in the middle of it. He was working for the CIA and wrote a book about the bungled policy, Decent Interval, which the U.S. government hated so much, it prosecuted him with the same kind of vehemence now turned on Edward Snowden and other whistleblowers. What are the lessons Snepp learned from Vietnam? Trying to buy off insurgents and local leaders rarely works. They “identified with their American bagmen, not with Vietnam’s central government,” Snepp wrote in a Los Angeles Times op-ed in May, “and the government in turn remained suspicious of their loyalties.” Moreover, assassination programs are a bad idea. Local sources manipulate lethal intelligence to settle scores. Innocents get blown away. Today drones carry out “targeted killings,” says Snepp; in Vietnam the organized murder campaign was called the Phoenix program.