An August 1968 photo of Richard Nixon, left, on a boat owned by his friend Charles “Bebe” Rebozo, right, in Key Biscayne, Florida. (Arthur Schatz/ARTHUR SCHATZ/TIME & LIFE PICTURES/GETTY IMAGES))

Richard Nixon was many things — crafty, criminal, self-pitying, vengeful, paranoid. But gay?

According to a book to be released Tuesday, “Nixon’s Darkest Secrets,” the former president and his best friend, Charles “Bebe” Rebozo, had a relationship of a “possibly homosexual nature.” But author Don Fulsom, a former radio reporter who covered the White House from Lyndon Johnson’s presidency to Bill Clinton’s, provides scant evidence for this claim. No new White House tapes. No love letters, incriminating pictures or diary entries. No recently declassified government documents. Just a recollection from retired journalist Bonnie Angelo, who, in an interview with me, confirmed the story she told Fulsom: In 1972, she saw a tipsy Nixon pull Rebozo into a group photo at a Florida restaurant and hold his hand for “upwards of a minute.”

That’s pretty thin gruel — but not so thin that it keeps the author from enthusiastic speculation. “Was Nixon’s tough-guy attitude toward gays just a cover for his own homosexuality, bisexuality or asexuality?” Fulsom writes. “Well, he isn’t still called ‘Tricky Dick’ for nothing.”

The book attempts to buttress the homosexual allegation by repeating rumors that the twice-divorced Rebozo, known as a ladies’ man, was gay. But this claim is secondhand, based on another controversial Nixon book, by author Anthony Summers, that was widely criticized for relying on second- or third-hand sources of dubious credibility. Fulsom provides no independent verification of the sketchy assertion.

Some stories are too good to be true. Others, evidently, are too good to check.

Still, the flimsy report of Nixon’s “gay affair” went viral on the Internet last month after galleys were leaked ahead of the book’s release. When I asked Fulsom about the media reaction, he said that accounts describing his “explosive revelations” that Nixon “carried on a sizzling gay love affair” exaggerated his findings, and he admitted that, without any photos showing Nixon and Rebozo in flagrante delicto, there is “no evidence it actually happened.”

But he defended his sourcing: “As a reporter, it was my duty to convey everything I learned,” including “another layer, if it’s true, of a very complicated guy who was into duplicity like no one else.”

This is not, in short, the kind of documentation that would survive vetting in any top-tier newsroom, let alone pass scholarly muster in a serious history journal.

Nixon is just the latest target of what writer Joyce Carol Oates has called “pathography” — a biographical genre devoted to digging up dirt. It’s the literary opposite of hagiography, which glorifies and celebrates its subject. Pathography’s “motifs are dysfunction and disaster, illness and pratfalls, failed marriages and failed careers, alcoholism and breakdowns and outrageous conduct,” Oates noted in 1988. “Its scenes are sensational, wallowing in squalor and foolishness; its dominant images are physical and deflating.”

America’s uncontested queen of pathography is Kitty Kelley, the best-selling muckraker of celebrities and political figures (or both, as when she implied, but failed to prove, that first lady Nancy Reagan had a sexual liaison with Frank Sinatra in the White House, a claim the Reagans denied).

Trailing behind is author Joe McGinniss, who wrote that Sarah Palin had a one-night stand with future NBA star Glen Rice and had an extramarital affair in the mid-1990s, and that she snorted cocaine off an oil drum during a snowmobile outing in Alaska. These claims were as widely circulated as they were thinly sourced and denied by Palin.

Still, at least Kelley and McGinniss focused on the living, who were around to deny the charges. Dead men can’t talk, let alone sue, so they make particularly inviting targets for historical speculation.

Take Abraham Lincoln. He, too, was the subject of a book arguing that he had male lovers. James Buchanan, America’s only bachelor president, has been the target of similar chatter since the 1850s. Yet there is almost no way to prove — or disprove — alleged intimacies from so long ago.

Then there is J. Edgar Hoover, the legendary FBI director, who has been described as having attended orgies with teenage boys while wearing a red skirt, a black feather boa, lace stockings, high heels, a black curly wig, makeup and false eyelashes. (Summers, the author who was Fulsom’s source that Nixon pal Rebozo was gay, also dug up this far-fetched tale.)

Although the Hoover-in-drag rumor has been widely discredited, it has nonetheless entered popular folklore — poetic retribution against the homophobic G-man whose sex-filled dossiers terrorized Washington for half a century. Even the sympathetic Clint Eastwood incorporated a sanitized version of this yarn in his recent “J. Edgar” biopic.

Film directors, publishers and writers produce such stories because they sell, often handsomely. And the public craves them because they are entertaining and help people feel better about their own messy lives.

Gossip — whether over a neighbor’s picket fence, in books and movies, or online — helps define social norms as we tut-tut about what behavior is acceptable and what is out of bounds. Rumor-mongering even performs an important leveling function in a democratic society, giving the lowliest of citizens the subversive power to sully even the most exalted reputations.

Conspiracy theories often fuel pathographies. The Kennedy family alone has generated a cottage industry of authors, screenwriters and producers peddling fiction as history. Hundreds of books and thousands of articles have been devoted to John F. Kennedy’s assassination. (In his new book, Fulsom recycles an outlandish rumor that Nixon conspired with the mafia to have JFK killed.) Other tracts have linked the Kennedys to Marilyn Monroe’s suicide, which some writers claim was actually murder by poisoned enema.

It’s almost impossible to refute such tales. After all, contradictory testimony can easily be dismissed as part of the conspirators’ diabolical cover-up. No telltale bullet casings recovered from the grassy knoll in Dallas? Well, that must be because the second gunman removed every scrap of evidence as part of the nefarious cabal.

Still, conspiracy theories, like pathographies, serve a purpose. Big events seem to demand big explanations, real or imagined. Conspiracy theories offer coherent causes for complicated and scary incidents; they reassure that life isn’t random and chaotic but planned by larger forces. They supply enemies to hate.

Most of all, as New York Times columnist Gail Collins points out in her book “Scorpion Tongues,” gossip — conspiratorial or otherwise — reflects what is troubling our culture at the moment: from alcohol or racial mixing to immigration or gender roles. It is no accident that the recent frenzy of historical gay “outings” — whether of Lincoln or Hoover or Nixon — is taking place when homosexuality has come out of the closet and same-sex marriage has become a prominent part of the legislative agenda in many places.

Historical revisionism does have its place. New facts — such as DNA evidence strongly suggesting that Thomas Jefferson fathered children with his slave Sally Hemings — can crucially change our understanding of events. “Every generation of historians has its distinctive worries about the present,” Arthur M. Schlesinger Jr. observed in 1986, “and consequently its distinctive demands on the past.”

The problem comes when revisionism is oblivious to facts, when profiteering trumps proof. Then, this kind of history resembles pornography, exciting and titillating, but debasing to the audience and subject alike.

Even Richard Nixon deserves better than that. He may have been queer, but not that kind of queer.

Mark Feldstein, the Richard Eaton professor of broadcast journalism at the University of Maryland, is the author of “Poisoning the Press: Richard Nixon, Jack Anderson, and the Rise of Washington’s Scandal Culture.”