Hubert H. Humphrey was the leading Minnesota political figure of his era, from the 1940s to the 1960s, during which decades he served as Minneapolis mayor, Minnesota’s U.S. senator, vice president of the United States and, in 1968, the first Minnesotan ever to be a major party presidential nominee.

That presidential campaign turned into a dramatic snakebit tale featuring the tragedy of the Vietnam War, the tortured, abusive relationship between President Lyndon B. Johnson and Vice President Humphrey, and the winner of that 1968 election, Richard Nixon, who during that campaign engaged in actions that some have called treason, in order to defeat Humphrey.

Specifically, Nixon used back-channel communications with the leaders of South Vietnam to discourage them from participating in peace talks that LBJ hoped would end the war. Through his secret envoy, Anna Chennault (and in violation of various laws and norms), Nixon discouraged South Vietnam from making that deal.

A last-minute announcement by the South Vietnamese President Nguyen Van Thieu that he would not attend the Paris peace talks reversed Humphrey’s late momentum in the polls, and Nixon beat Humphrey by less than 1 percent of the popular vote (although the electoral vote margin was larger).

At a recent University of Minnesota-Humphrey School event, the featured speaker — Stuart Eizenstat, a veteran of both the Humphrey 1968 campaign and the subsequent Carter-Mondale administration — suggested that Humphrey knew of Nixon’s illicit interference in Vietnam during the 1968 campaign, but didn’t make it public because he was too Minnesota nice to do so.

I covered the Eizenstat event, and wrote about the “too nice” explanation, with some skepticism.

In the following days, I asked former Vice President Walter Mondale whether he could corroborate the “too nice” anecdote. Mondale, a Humphrey protégé and, in 1968 a rising star in the U.S. Senate, said no, he couldn’t corroborate that “too nice” bit, and added that it made no sense to him. There was nothing Minnesotan nor “nice” about allowing Nixon to profit politically from interfering with U.S. efforts to end the Vietnam war.

Mondale even reached out to some of the other surviving veterans of the ’68 campaign to ask what caused Humphrey to hold back. But he didn’t come up with a clear final answer.

Meanwhile, I heard from historian Arnold Offner, author of an excellent new Humphrey biography (“Hubert Humphrey: The Conscience of the Country,” published by Yale University Press) that tells this tale of the last days of the 1968 campaign in eye-watering detail, with footnoted sources for every fact. In an email to me, Offner specifically rejected the “too nice” explanation and offered his own take. My main goal in returning to the topic so soon is to provide some of Offner’s very interesting findings.

For one, as to the question of why Humphrey didn’t make public in the last days of the campaign what he knew of Nixon’s back-channel interference with efforts to end the Vietnam war, Offner calls attention to a lie that LBJ told Humphrey.

Johnson did tell Humphrey what Nixon was doing, but added that he had “no hard proof” of Nixon’s illicit backchannel efforts to prevent progress toward peace. In reality, LBJ had transcripts of FBI phone taps proving it.

But, Offner suggested to me, Humphrey understood LBJ’s “no hard proof” statement to mean that LBJ wouldn’t make the tapes or transcripts available to Humphrey, and that if Humphrey went public with the charge, he would not be able to prove the allegation.

Offner also makes a larger argument that the LBJ-HHH relationship had been an ugly, confusing mess ever since Humphrey agreed to be LBJ’s running mate for the 1964 election. When LBJ was in the process of looking for a running mate, he told his intimates that it was important to “have his pecker in my pocket.”

Humphrey, who had been a highly respected senator and who deeply wanted to be president, believed the vice presidency was his best route to that goal.

LBJ demanded total loyalty from HHH, while giving little in return. He frequently berated Humphrey for any small or imagined offense. (The details of Johnson’s pecker-pocketing mistreatment are excruciating.)

Humphrey did write a memo to LBJ early in their term, which seems to be full of wisdom about how to avoid a quagmire in Vietnam. LBJ ignored the advice and cut Humphrey out of future meetings on Vietnam policy.

Humphrey’s response was to double down on loyalty to LBJ, to the point of accepting humiliation, confiding in one memo to a colleague: “From now on out there are no Humphrey rooms, there is no Humphrey staff, there is no Humphrey program, and there are no Humphrey ideas. From now on, there simply isn’t any Humphrey.”

And, whatever private doubts he may have harbored about the U.S. escalation in Vietnam, Humphrey publicly supported administration policy so thoroughly that it’s hard find any further evidence, after that early memo, that he harbored doubts.

Offner relays one hideous incident in which LBJ commanded Humphrey to recite aloud for him his recent speech in favor of the Johnson’s Vietnam policy, then walked into the bathroom to defecate and, while sitting on the toilet, hollered through the open door: “Keep talking Hubert, I’m listening.”

It’s hard to know how deep into his heart Humphrey’s conversion from dove to hawk went. Offner quotes some Humphrey remarks, after this period, in which he suggested by staying within the Johnson circle, his pro-war views were constantly reinforced. In my conversation with Mondale, he said with evident regret that Humphrey would have had a different view, and the freedom to express it, if he had stayed in the Senate.

Of course, LBJ then shocked the country by deciding not to seek re-election in 1968. But he still had sufficient leverage over Humphrey that HHH, running for the Democratic nomination to replace Johnson, publicly supported LBJ’s increasingly unpopular Vietnam policy even as he was challenged by two anti-war Democrats, New York Sen. Robert Kennedy and Minnesota Sen. Eugene McCarthy. Humphrey refused to debate them about the war. Kennedy, of course, was killed before the convention in Chicago.

I’m not sure I ever heard about this before, but Offner writes that LBJ was secretly scheming with Chicago Mayor Richard Daley to invite him to make a surprise address to the Chicago convention, and harbored hopes that such an appearance might actually stampede the convention to re-nominate him for another term. Nothing like that happened, but if LBJ really believed it might, it could explain his motivations for doing so much to undermine Humphrey’s candidacy.

There was also an effort by Humphrey and others to get a moderate Vietnam peace plank into the Democratic platform, which might have helped Humphrey begin to separate himself from the unpopular war. But that, too, was vetoed by LBJ.

Of course, peace protests and violent suppression of those protests by Chicago police outside the nominating convention got Humphrey’s candidacy off to a terrible start, and he trailed in the polls all year, generally by double digits. The above developments led Offner to believe that LBJ may have actually been hoping that Nixon would beat Humphrey, and Humphrey wondered the same. Writes Offner:

Humphrey left the Democratic convention trailing Nixon in polls by 16 or more points and subject to Johnson’s continued harassment. The vice president admitted to Soviet ambassador Anatoly Dobrynin: “I don’t even know who Johnson would prefer as the next president, Nixon or me.” Similarly, Defense Secretary Clark Clifford wondered on more than one occasion whether, in his “heart of hearts, Lyndon Johnson really wants Humphrey to win.”

(As I mentioned, Offner footnotes every factual assertion and quote. Dobrynin and Clifford both said what is suggested above in their own memoirs.)

Why would Democrat LBJ prefer Republican Nixon over Democrat Humphrey? I asked Offner.

His answer had several layers, including the psychological. LBJ was brilliant and successful but knew he was not well liked by the country. Nor was Nixon. Humphrey was among the most likable figures in Washington. LBJ seethed at the thought of being replaced by someone whom the country so clearly liked better than himself. Whether that is true or false, LBJ did very little to help Humphrey win, and a lot to make it more likely that Humphrey would lose, including insisting that Humphrey toe his unpopular line on Vietnam.

Nixon also cultivated LBJ. As Offner relates, Nixon sent the Rev. Billy Graham as an emissary to LBJ with a written message, which Graham read to Johnson point by point, including a promise to do nothing after the election to embarrass LBJ, to make sure LBJ got “a major share of the credit” for the end of the Vietnam war, whenever that came about.

But the climax of this dark tale comes late in the campaign. LBJ had been working to arrange peace talks, in Paris, among the warring parties in Vietnam, and announced shortly before the election that he would suspend U.S. bombing of North Vietnam to improve the chances of success in those talks. As the situation in Vietnam seemed more promising, Humphrey began to rise in the polls, cutting Nixon’s lead to single digits and improving fast.

Nixon wanted to scuttle the momentum toward peace, for obvious political reasons, but any such interference could be considered treasonous.

Anna Chennault, a Republican activist (and widow of a famous U.S. Air Force hero) was working to prevent the Paris talks from succeeding, and (at Nixon’s bidding) told South Vietnamese President Nguyen Van Thieu not to go to the Paris Peace Talks but to wait until Nixon was in the White House and he would secure a better deal for Thieu. In the key final days of the 1968 campaign, Thieu’s announcement that he would not go to Paris interrupted Humphrey’s late surge.

But the FBI was illicitly taping Nixon’s calls with Chennault, and LBJ had tapes and transcripts of the calls. No one can prove this, but if LBJ had made these tapes and transcripts public, it might – and many believed would – have tipped the election to Humphrey. Instead, as I mentioned above, LBJ told Humphrey that he had no hard proof of Nixon’s activities.

I mentioned above that Nixon’s activity to interfere with the efforts of the U.S. president to end a war in which U.S. troops were getting killed might be “treason.” I say it might be, but Mondale didn’t use that word and urged me to be careful about such a serious charge. So I have.

But I’ll close with this, from the Offner book but footnoted to a biography of Madame Chennault. In the last days of the campaign, after Thieu, taking the advice of Chennault, had announced that he would not go to the Paris peace talks, the FBI intercepted a message from Chennault to South Vietnamese Ambassador to Washington Bui Diem. Chennault said that “her boss” (Offner believes this referred to Nixon’s running-mate, Spiro Agnew) had just called her to tell her to tell Thieu to “hold on. We’re gonna win.”

Johnson didn’t call Nixon to complain, nor Humphrey to put him in the picture. But he did call Sen. Everett Dirksen, the leader of the Senate Republican caucus, and told him about the intercept. And Johnson told Dirksen that it would “shock America” to learn that Nixon’s agent was colluding against the president’s efforts to wind down a war in which U.S. troops were dying.

“This is treason,” LBJ told Dirksen, to which Dirksen, the Republican leader, replied: “I know.”