In October 1968, during the Paris Peace Talks, the U.S. was ready to agree to cease bombing Hanoi, the capital of North Vietnam, in exchange for concessions that would halt the decades-long conflict which eventually killed an estmiated 58,000 American soldiers, 2 million Vietnamese civilians and 1.1 million North Vietnamese and Viet Cong combatants. But suddenly, the day before the 1968 presidential election, a close race between Hubert Humphrey and Richard Nixon, South Vietnam inexplicably walked away from the negotiating table. Direct U.S. military involvement in the war lasted another five years.

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For decades, rumors have swirled that Richard Nixon’s presidential campaign had interfered in the Vietnam peace negotiations by sending a messages through Nixon aide Anna Chennault to the South Vietnamese embassy and on to President Nguyen van Thieu. The Nixon campaign, it was rumored, promised the South Vietnamese bigger concessions if they waited to negotiate peace until after Nixon was elected. The idea was to not give President Lyndon Johnson and Humphrey a PR victory by suspending the war before the election.

Now, political biographer John Farrell, writing in The New York Times' opinion section this weekend, reports that handwritten notes from Nixon’s future White House Chief of Staff, H.R. Haldeman show evidence that the 36th president tried to secretly influence the peace talks while still a presidential candidate and a private citizen.

Throughout his lifetime Nixon and his aids vociferously denied that he would do any such thing. “My God. I would never do anything to encourage” South Vietnam “not to come to the table,” Nixon is heard telling Johnson in a conversation taped in the White House, reports Farrell.

But over the years, more information about the incident leaked out. According to David Taylor at the BBC, in 2013 declassified tapes from Johnson’s White House show that the FBI had intercepted Chennault’s calls to the South Vietnamese ambassador telling them to “just hang through the election.” Johnson also ordered the FBI to surveil the Nixon campaign and to figure out if Nixon was personally involved in the back channel operation.

Taylor reports that Johnson became convinced that Nixon knew about the ploy and even sent the candidate a message through Senator Everett Dirksen telling him to back down and that he was engaging in treason.

Though the Johnson administration debated going public with the information before the election, they decided against it because they lacked “absolute proof” that Nixon was personally involved, writes Farrell. Taylor reports they were also afraid of revealing that the FBI was intercepting calls from the South Vietnamese ambassador and Chennault, a U.S. citizen, and that NSA was also monitoring communications.

The handwritten notes from Haldeman, however, seem to corroborate the idea that Nixon knew about the plan and personally ordered Chennault to communicate with South Vietnam. The notes were taken by Haldeman on October 22, 1968, during a phone conversation with Nixon. They include Nixon’s orders to “Keep Anna Chennault working on” South Vietnam, and also say: “Any other way to monkey wrench it? Anything RN [Richard Nixon] can do.” The notes also show Nixon wanted to have nationalist Chinese businessman Louis Kung also pressure president Thieu not to accept a truce. The notes indicate Nixon wanted his running mate Spiro Agnew to pressure C.I.A. director Richard Helms and that they campaign sought to get Taiwanese president Chiang Kai-Shek involved.

Farrell reports that the notes have actually been available since the Nixon Presidential Library release them in 2007. But Farrell only realized the content of the handwritten notes about what has become known as The Chennault Affair while researching a new biography of Nixon.

While it’s likely that the revelation of Nixon’s involvement might have influenced the outcome of the 1968 American election, Jack Torry reports for Politico that the Paris Peace Talks were likely on the ropes before November 1968, and that the North Vietnamese were not serious about ending the war. Transcripts from the time show that South Vietnamese President Thieu was not willing to participate in talks that included the National Liberation Front, the communist party trying to overthrow the South Vietnam government.