Forty years ago this month, when National Security Adviser Henry Kissinger took a secret trip to China that would turn him into an international celebrity overnight once it was revealed, President Richard Nixon quietly sold South Vietnam down the river for political gain.

It's a sordid story, too long kept secret, but it needs to be told today, when the editor of Foreign Affairs in the pages of the New York Times actually urges President Obama to model his exit from Afghanistan on Nixon's exit from Vietnam.  That's a formula for political triumph at the cost of geopolitical failure, moral squalor and human devastation.

"We want a decent interval," Kissinger scribbled in the margins of his thick briefing book (as historian Jeffrey Kimball discovered).  "You have our assurance."

It's a strange phrase, nearly forgotten, but "decent interval" meant something in the latter days of Vietnam, when our leaders groped for a way to get out of the war without admitting they couldn't find a way to win it.  As Daniel Ellsberg wrote a few months before the secret trip, “During 1968, Henry Kissinger frequently said in private talks that the appropriate goal of U.S. policy was a ‘decent interval’—two to three years—between the withdrawal of U.S. troops and a Communist takeover in Vietnam."

This interval, it was argued at the time, would protect the nation's credibility from the humiliation of defeat.  But a transcript prepared by Kissinger's own aides of his first meeting with Chinese Premier Zhou Enlai reveals how willing Nixon was to sacrifice America's credibility abroad to preserve his political credibility at home.  As Kissinger explained it, the president would agree to complete withdrawal of American troops in return for Hanoi's release of American prisoners of war and a ceasefire ("say 18 months or some period").

"If the agreement breaks down, then it is quite possible that the people in Vietnam will fight it out," Kissinger said (as historian Jussi Hanhimaki found).  "If the government is as unpopular as you seem to think, then the quicker our forces are withdrawn, the quicker it will be overthrown.  And if it is overthrown after we withdraw, we will not intervene."

Wait a minute—why haven't you ever heard any of this before?  For many reasons, none of them good.  First, Nixon deliberately misled the public.  When the president revealed Kissinger's trip to China and announced his own forthcoming public one on national television, he spoke of "a lasting peace in the world," not the temporary peace in Vietnam he was secretly negotiating.  "Our action in seeking a new relationship with the People's Republic of China will not be at the expense of our old friends."

Second, most conservatives took Nixon at his word, although some objected that Republicans would be up in arms if a Democratic president had announced he was going to China.  "Of course we would," California governor Ronald Reagan said.  "Democratic presidents lacked the will and wisdom to exact a victory as the price for the young Americans who died in Vietnam.  But this is a Republican president who has said only, 'I will go and talk. I have no intention of abandoning old friends.'"  Reagan was an optimist, if only about his own party.

Third, liberals shared the conservative certainty that America's foremost anti-Communist politician wouldn't abandon South Vietnam.  One of the reasons Ellsberg, a former Defense Department analyst, leaked the Pentagon Papers, a Top Secret DoD history of the Vietnam War, was his conviction that Nixon was following the pattern of previous presidents and trying to establish an indefinite fighting stalemate in Vietnam.  Likewise, former defense secretary Clark Clifford charged that Nixon planned "perpetual war."  And George McGovern, Nixon's 1972 Democratic opponent, framed the election as "a choice between four more years of war, or four years of peace."

Nixon profited greatly from the way liberals and conservatives alike overestimated his commitment to South Vietnam.  When Hanoi agreed to Nixon's terms shortly before Election Day 1972, knowing they would lead to Communist victory, Kissinger announced, "Peace is at hand."  Nixon won reelection by the largest popular margin of any Republican.

If only voters had heard what Nixon privately told Kissinger when a settlement first appeared within reach:  "I look at the tide of history out there, South Vietnam probably is never gonna survive anyway.  I’m just being perfectly candid."  Not with the American people.  He promised "peace with honor," but delivered delayed defeat.  To avoid a South Vietnamese collapse before Election Day and for a "decent interval" after, Nixon sacrificed 20,000 American lives.

The bipartisan consensus that Nixon would continue to use military means to prop up Saigon obscured the crucial ways his own settlement terms made that impossible to do.  As the Pentagon, State Department and CIA informed the President in his first year in office, the South could not handle both the Vietcong and North Vietnamese army "without U.S. combat support in the form of air, helicopters, artillery, logistics and major ground forces," yet Nixon's settlement removed all U.S. ground forces. Total withdrawal was the price Hanoi exacted for release of American POWs.  Those who continue to insist that Nixon could've maintained an anti-Communist regime in Saigon after the settlement using U.S. airpower alone have never explained what he was supposed to do once the North Vietnamese resumed shooting down planes and taking Americans prisoner.  At that point, Nixon would have nothing sufficiently valuable to trade for the release of POWs—nothing but overt surrender (as opposed to the disguised surrender of the "decent interval").

Fourth, Nixon shifted the blame for defeat in Vietnam onto Congress shortly after the last troops and POWs came home.  On June 29, 1973, he informed Congress that he would accept a complete ban on U.S. military action in all of Indochina (Vietnam, Laos and Cambodia) even though (1) Republican, Democratic and neutral vote counters agreed he had enough support to sustain a veto of such a bill (2) earlier that week Congress had sustained his veto of a weaker bill covering just Laos and Cambodia.  Nixon claimed Congress tied his hands, but he tied his own.  Most people didn't realize that this smooth move enabled Nixon to live up to the secret assurances he had given the Communists through Kissinger that he wouldn't intervene if they waited a "decent interval" before conquering the South, because...

Fifth, Nixon fought for the rest of his life to keep his record from the public.  The briefing book and transcript quoted above remained classified for decades, until most people forgot what "decent interval" meant.  Sixth, in 2005 the Richard M. Nixon Library & Birthplace, at the time still a private, partisan, political shrine, cancelled a long-planned academic conference on Nixon and Vietnam, sparking an uproar.

Things have come full circle at the Nixon Library, which has invited many scholars from that notoriously cancelled conference to present their research at its first scholarly symposium since joining the National Archives' presidential library system under the excellent stewardship of director Timothy Naftali.  It's not a moment too soon for the public to hear from scholars like Jeffrey Kimball, who has done more than any other historian to bring to light Nixon's strategy of postponing, rather than preventing, Communist victory.  The temptation for politicians today to prolong wars they can't win and fake "peace" settlements that won't hold must be as strong as it was for Nixon and Kissinger four decades ago, but if enough patriotic Americans learn this dark history, we will not be forced to repeat it.