WASHINGTON — There’s little doubt Richard Nixon was up to dirty tricks before his presidency ever began.

Documents released by the National Archives’ Nixon Presidential Library on Wednesday add weight to considerable, existing evidence that his 1968 presidential campaign tried to sabotage Vietnam peace talks before the U.S. election. The apparent purpose: to deny his Democratic challenger, Hubert Humphrey, a political advantage in the tight race to succeed Lyndon Johnson in the White House.

The documents contain a memo written to Nixon by his aide Tom Charles Huston in 1970, looking back at the so-called Chennault Affair, named for Anna Chennault, a Republican activist who had ties to South Vietnam leaders. Chennault was thought to have been a secret GOP emissary, conveying messages from the Nixon campaign to the South Vietnamese that they should resist peace talks with North Vietnam because they would get a better deal if they waited for Nixon to become president.

Johnson was incensed by what he regarded as Nixon’s meddling, as a candidate, in Vietnam War policy. At one point he called Nixon treasonous. Federal law prohibits private citizens — which Nixon then was — from interfering in U.S. diplomacy.

Nixon’s people saw the episode differently. They thought LBJ was calling a bombing halt and encouraging peace talks merely to give fellow Democrat Humphrey a boost in the election. And they thought he was using the heavy hand of government surveillance and intimidation to get to the bottom of what the Nixon campaign was doing with the South Vietnamese — tactics Nixon’s men would practice ruthlessly against real and perceived adversaries once in office.

Huston’s report to Nixon emerged in thousands of pages of documents from the Nixon administration released at the presidential library in Yorba Linda, California, with a small sample available online.

The full contours of the renegade Republican diplomacy in 1968 were not uncovered at the time, and they are not all exposed in Huston’s account, which was more concerned with investigating LBJ’s response to the secret GOP contacts than with the contacts themselves. But historians have pieced much of the story together over the years from various sources.

In an oral history released by the National Archives last year, Huston voiced his conviction that Nixon’s campaign manager, John Mitchell, was directly involved in the episode and that it was likely Nixon at least knew about it. In his 2014 book, “Chasing Shadows,” Nixon historian Ken Hughes asserted that Nixon, fearing exposure of his 1968 machinations, wanted operatives to break into the Brookings Institution think tank to steal Chennault Affair documents that he thought were there.

That break-in did not happen. But another one did — the politically-driven burglary at the Watergate offices of the Democratic Party, touching off the scandal that destroyed Nixon’s presidency in 1974.

Only subscribers are eligible to post comments. Please subscribe or login first for digital access. Here’s why.

Use the form below to reset your password. When you've submitted your account email, we will send an email with a reset code.