I take on JFK and what thanks do I get?

This was a book for which the omens could not have been more promising: an investigation of America's most beguiling modern president by one of its most renowned reporters. Now in the shops, it has indeed met with an astonishing reception; astonishing in its vitriol.

Seymour Hersh protests that he knew what kind of storm his latest tome, an unrelenting assault on the character, morals and integrity of John F Kennedy, would unleash. While others question the veracity of claims in The Dark Side of Camelot, it is Hersh's alleged stoicism that is the hardest to believe.

What must hurt him more: the comparisons being made of him with the sometime controversial film-maker Oliver Stone and muck-raking author Kitty Kelley; the suggestion that he has succumbed to the lure of mega-bucks in the form of advances, royalties and television deals; or simply the sheer weight of opprobrium being unloaded upon him by peers in his own profession?

"Cartoon of a retouched picture of John F Kennedy," raged the Boston Globe. "A case study in how not to do investigative reporting," said a review in the Washington Post. And atop a cover story about Hersh in Time magazine: "How believable is his controversial new book?"

Anyone familiar with American journalism will know that Hersh is a Hercules among reporters. True, he has not been flattered by a film about his exploits as the Watergate sleuths Bob Woodward and Carl Bernstein have, but the idea of mentioning Kelley and Hersh in the same breath would hitherto have been inconceivable.

Hersh gained fame with his unearthing of the Mylai massacre in Vietnam in 1969, when American GIs slaughtered scores of Vietnamese far from the eye of the public. For that he won a Pulitzer prize for investigative reporting. Thereafter, Hersh eschewed the Washington schmooze-scene and applied his zealous skills to uncovering abuses of the powerful. As well as being a star reporter for the New York Times in Washington through the Seventies, Hersh has written three books: one skewering the role of Henry Kissinger in the Nixon administration; another probing the downing of the Korean jumbo jet by Moscow; and a third about domestic spying by the CIA.

Of course any debunking of the late JFK, who, almost inexplicably, remains the most fervently admired of any of the American presidents by US citizens with the possible exception of George Washington, is always going to attract criticism. Hersh is not the first to explore the more unedifying qualities of the late President, but no previous biography has come close to this for purity of poison.

After five years of research, Hersh offers a gawdy canvas of Kennedy sleaze over some 450 pages. There is sex galore - references to orgies in the White House swimming pool and JFK's apparent appetite for, as one Hersh source puts it, "a strange piece of ass every day" are wickedly salacious. British readers may especially enjoy a description of mild panic in the White House over the Profumo affair as Washington wonders whether its Soviet tentacles might somehow join with the President's own liaisons.

Other chapters address issues more pertinent to JFK's office. Some are familiar - a fact that has opened Hersh to criticism that he has simply wallowed in old slime-pits - some less so. These include the alleged attempt by JFK to steal the vote in 1960 in Illinois with the help of the Chicago Mafia; a plot headed by the President himself to arrange the assassination of Fidel Castro; and a foul-up whereby Kennedy allowed himself to be bribed into awarding a giant defence contract to General Dynamics. Add to all of that the President's accumulated suffering from a variety of venereal diseases and a secret, never-annulled, previous marriage.

Some of those attacking Hersh may have their own reasons. Another prominent American journalist and a former Washington correspondent for Time, Hugh Sidey, calls the book "evil", claiming that some reporters "come to act like and resemble those they investigate - people who are swayed by money, willing to use any means to their ends and are secretive and conspiratorial". Sidey was among the inner circle of journalists who covered the Kennedy White House (and who, if Hersh is even half right, missed the story). Even the historian Arthur Schlesinger has termed the book the "most obsessive book imaginable" and a "triumph in gullibility". But then we should remember that Schlesinger served as an aide in the JFK White House.

The stampede to indict Hersh has been deafening. Even the review in the New York Times, Hersh's erstwhile home, concluded that the book shows not so much the dark side of Camelot but the dark side of the author. Priscilla Painton, editor of the Time story, said: "There is an increasing amount of crap that gets put out with a kind of nominal nod in the direction of good history and good journalism but with a desperate lurch for the best-seller list."

Most embarrassing have been the assaults on the credibility of Hersh's sources. It does not help that four former secret service agents, who provided most of the sexual allegations, have all been denounced by another agent in the White House at the time. And Hersh himself admits that the person purporting the early Kennedy marriage suffers from short-term memory loss.

Especially damaging, however, was the brouhaha triggered a month ago by news that a whole chapter about JFK and Marilyn Monroe had to be excised at the last minute when the source material - letters to Monroe from JFK offering her $600,000 to stay quiet about an affair between them - turned out to have been rather obvious fakes. NBC, the TV network, has since revealed that it backed out of a deal to make a film of the book because of suspicions it had about the letters. Happily for Hersh, ABC subsequently filled NBC's shoes and will air a two-hour special based on the book in two weeks.

The obligatory round of press, radio and television interviews has forced Hersh to defend himself. And he has, unflinchingly. He believes that if the Kennedy clan is not behind the fusillade against him, then it is the work of other enemies he has made. "It is not hard to find a lot of people who don't like me. I've spent a lot of time making people angry. I've been there. Hard stories produce a lot of anger."

"I knew I would be castigated forever," he told the Detroit News, insisting that there was an honourable purpose in writing the book. "It's important to know the President's character. I was convinced that there was a direct line between the recklessness in Kennedy's sexual behaviour and his foreign policy, particularly in Cuba and the Bay of Pigs."

Stand back from the ruckus and two cliched adages spring to mind. One, of course, is "who needs enemies when you have friends like these". And the other? "All publicity is good publicity." Even Ms Kelley must be turning a shade of green over the exposure that Mr Hersh and The Dark Side of Camelot are receiving. Early figures suggest the book is selling well. And the ABC show is still to come.