After March 31st, the primaries became a mano a mano between Kennedy and McCarthy. As a campaigner, Kennedy was hot and McCarthy was cool, but McCarthy did not suffer from the contrast, at least among white liberals. He had established his own aura, the aura of the samurai: unswerving and ascetic.

On May 28th, he defeated Kennedy in the Oregon primary. It was the first time in twenty-seven consecutive races that any Kennedy had lost an election. On June 5th, Kennedy rebounded and won the big one, California. Minutes after declaring victory, he was shot in the Ambassador Hotel, in Los Angeles. He died the next day, along with the seeds of whatever future America he carried within him.

All the antiwar fury in the Democratic Party could now focus its hopes on McCarthy. I went with my family to see him on July 25th at an enormous rally at Fenway Park, in Boston. McCarthy’s wife, Abigail, who was closely involved in the campaign, defined McCarthy’s constituency as “academia united with the mobile society of scientists, educators, technologists and the new post-World-War II college class.” If that was your base in 1968, Fenway Park was the ideal place to address it.

Almost forty thousand people were jammed into a stadium whose official capacity is under thirty-eight thousand; five thousand more listened outside. McCarthy was introduced by Leonard Bernstein, a man practiced in podium histrionics. I can still hear him cuing McCarthy’s entrance—“Even now, entering from the center-field bleachers . . .” A door opened under the stands, and McCarthy walked across the field to a speaker’s platform at second base.

McCarthy had adopted the rhetoric of revolution. It was to be a revolution of reason and common sense, of course; McCarthy was a Midwesterner and a Catholic. He loathed the yippies and the student radicals; his student volunteers were encouraged to go “clean for Gene.” But the language of revolution was what you used to mobilize antiwar liberals in 1968. So McCarthy spoke at Fenway about the “power of the people” and called his campaign “a kind of uprising.”

McCarthy had a wry and slightly professorial tone. “Almost everything that the Church tried to give up at the Vatican Council has been picked up by the Defense Department,” he said at one point. I don’t think that line would have meant much in Cleveland, but it received knowing chortles and applause in Boston.

He got his loudest and most sustained reaction when he mentioned the Convention, then one month away, in Chicago. “Any visit to Chicago is always beset with some uncertainties, some dangers,” he said (applause indicating that understatement was always appreciated), “but I think that we shall succeed there.” He said it in the most nonchalant tone of voice imaginable, but the cheers went on and on.

Those were the cheers of desperation, tribute to a valiant effort doomed to come up short. Everyone at Fenway knew that McCarthy did not have the delegates. He would have to inspire a stampede at the Convention to rip the nomination from Humphrey, who stood to inherit Johnson’s delegates. In the minds of everyone who was old enough, there probably flickered the memory of a speech that McCarthy had delivered at the 1960 Democratic Convention, putting Adlai Stevenson’s name in nomination. “Do not leave this prophet without honor in his own party,” McCarthy had said, setting off a floor demonstration that threatened to steal the Convention from J.F.K. But lightning was not likely to strike twice, and in 1960 Kennedy won on the first ballot, anyway.

We watched every minute of the 1968 Convention in our basement, and there were some very late nights. What everyone remembers are the attacks by police and National Guardsmen on demonstrators in the streets outside. In fact, the networks did not devote much time to covering those. Out of thirty-eight hours of Convention coverage, CBS devoted thirty-two minutes to the demonstrators. NBC devoted fourteen minutes out of nineteen hours of coverage.

But the scene inside the hall—the Chicago Amphitheatre, on the South Side, near the stockyards—was tumultuous enough. The CBS reporters Dan Rather and Mike Wallace were roughed up by security personnel. After a vote on an antiwar platform plank failed, members of the New York delegation joined arms and sang “We Shall Overcome.” When Senator Abraham Ribicoff, of Connecticut, was giving a speech, the mayor of Chicago, Richard Daley, shouted at him, “Fuck you, you Jew son of a bitch, you lousy motherfucker, go home.”

The antiwar delegates lost every battle. A last-minute attempt to draft Edward Kennedy was aborted, and Humphrey won the nomination on the first ballot, with some seventeen hundred delegates, eight hundred and forty-seven more than the rest of the field.

The Convention left the Party fractured. McCarthy refused to endorse Humphrey, who began the fall campaign far behind in the polls. “Right now, you’re dead,” his campaign manager, Lawrence O’Brien, told him. He did come back, and nearly made up the difference. At the end of September, he at last broke with Johnson and announced that he would halt the bombing. At the end of October, McCarthy finally endorsed Humphrey. It was not quite enough. On November 5th, something happened that would have been unthinkable a few years earlier: Richard Nixon was elected President.

The story of this election has been told in many books, from Theodore H. White’s “The Making of the President 1968” and Lewis Chester, Godfrey Hodgson, and Bruce Page’s mammoth “An American Melodrama,” both published in 1969, to Michael A. Cohen’s “American Maelstrom,” which came out in 2016. It is featured in classic histories of the postwar period, including Hodgson’s “America in Our Time,” Allen J. Matusow’s “The Unraveling of America,” G. Calvin MacKenzie and Robert Weisbrot’s “The Liberal Hour,” and Todd Gitlin’s “The Sixties.” The story of the 1968 Presidential election is like oral poetry, a saga passed down from bard to bard that no one (or no one of a certain age, maybe) seems to tire of hearing.

Lawrence O’Donnell’s “Playing with Fire: The 1968 Election and the Transformation of American Politics” (Penguin) is the latest in this string of recitations. O’Donnell is the host of “The Last Word,” on MSNBC; he has worked on Capitol Hill, and he was a writer and producer for “The West Wing.” His book relies almost entirely on published sources, and so it adds little to what we know. But he is a talented storyteller, and his analysis of campaign tactics is sharp.

And the story of that election still matters. In 1968, Americans elected a man with some savvy and no principles. In 2016, they elected a man with neither. O’Donnell’s book makes it a little easier to understand how we got from there to here. It turns out that the distance is not all that great.