From a distance of nearly 50 years, the liberalism of 1960 is hardly recognizable. It was comfortable with the use of American power abroad, unabashedly patriotic and forward-looking. But that was before The Fall.

In his eye-opening new book "Camelot and the Cultural Revolution," Jim Piereson argues The Fall was the assassination of President Kennedy. It represented more than the tragic death of a young president, but the descent of liberalism from an optimistic creed focused on pragmatic improvements in the American condition to a darker philosophy obsessed with America's sins. Echoes of the assassination -- and the meaning attributed to it by JFK's admirers -- can still be heard in the querulous tones of contemporary liberalism.

The real John F. Kennedy wasn't the paladin of liberal purity of myth. He was friends with Joseph McCarthy. In his 1952 campaign for Senate and his 1960 presidential campaign, he got to the right of his Republican opponents on key issues. "Kennedy did not want anyone to tag him as a liberal, which he regarded as the kiss of death in electoral politics," Piereson writes. As president, he was vigorously anti-communist, a tax-cutter and a cautious supporter of civil rights.

His kind of liberalism -- "tough and realistic," as Piereson puts it, in the tradition of FDR and Truman -- was carried away in the riptide of his death. In a crucial and counterintuitive interpretive act, the nation's opinion elite made JFK a martyr to civil rights instead of the Cold War. Kennedy had been killed by a communist, Lee Harvey Oswald, who a few years before had tried to defect to the Soviet Union. Liberals nonetheless blamed the assassination on, in the characteristic words of Supreme Court Chief Justice Earl Warren, "the hatred and bitterness that has been injected into the life of our nation by bigots."

Thus, the assassination curdled into an indictment of American society: "Kennedy Victim of Violent Streak He Sought to Curb in Nation," read a New York Times headline. Until this point, 20th-century liberalism had tended to see history as a steady march of progress. Now, the march had been interrupted by the country's own pathologies. "Kennedy was mourned in a spirit of frustrated possibility and dashed hopes," Piereson argues, and that sense of loss came to define the new liberalism.

American history no longer appeared to be a benign process, but a twisted story of rapine and oppression. "With such a bill of indictment," Piereson writes, "the new liberals now held that Americans had no good reason to feel pride in their country's past or optimism about its future."

Their agenda took on a punitive edge, focused on compensating victim groups and expiating the country's guilt.

The left developed ambivalence about national power, in which the old liberal reformers had placed such faith. In the paranoid theories that sprang up in the wake of Kennedy's assassination -- many of them to avoid the simple, uncongenial fact that a lone communist had killed the president -- the seat of American government had been the locus of a secret plot to kill JFK. The conspiracy theories and anti-Americanism that had so appalled liberals about the far right in the 1950s had now gravitated to the left. Bizarrely, after a liberal hero was slain by a Marxist, communist icons and ideas became more fashionable on the left than ever before.

Other things were going on obviously, most importantly the Vietnam War. But the war was seen through the prism of American malignancy established by the Kennedy assassination. This downbeat and adversarial disposition is -- more than any specific policy weaknesses on, say, national security -- a drag on contemporary liberalism's long-term appeal. One day a Democratic politician will emerge who is compelling enough to vanquish the foul spirit of JFK's assassination from the left.

Until that happens, JFK has to be remembered, in Piereson's words, as "the last articulate spokesman for the now lost world of American liberalism."