When Tom Fiedler's phone rang the evening of April 27, 1987, he thought it might be another crank call, the kind political reporters get all the time. But Fiedler, a veteran campaign chronicler for the Miami Herald, couldn't ignore the caller's message: "Gary Hart is having an affair with a friend of mine."

At the time, Hart, a married U.S. senator from Colorado, was the front-runner for the 1988 Democratic presidential nomination. In announcing his candidacy two weeks earlier, he had vowed to hew to "the very highest standards of integrity and ethics," but he had since been besieged by rumors—all unsubstantiated—that he was a philanderer. Some of the innuendo had appeared in coverage by the mainstream media. Fiedler had deplored that practice in print, concluding in that morning's Herald: "In a harsh light, the media reports themselves are rumor-mongering, pure and simple."

"Those aren't rumors," Fiedler's caller told him that April evening.

Fiedler began investigating. Within days he found himself staking out Hart's town house in Washington, D.C.—and thinking, he recalls today, "This is nuts. What am I doing? This is not what a political journalist does."

Up until then, it wasn't. But the Hart saga would change the rules of the game.

Before the 1988 presidential campaign, American political reporters generally observed an unwritten rule: a politician's private life was private, absent compelling evidence that personal conduct was affecting public performance. It was considered no breach of duty when the press corps turned a blind eye to President John F. Kennedy's extramarital adventures—and left it to Senate investigators to discover, 12 years after his death, that the 35th president had shared one of his mistresses with a mob boss.

That all changed on Sunday, May 3, 1987, when Fiedler and his colleague Jim McGee told Herald readers: "Gary Hart, the Democratic presidential candidate who has dismissed allegations of womanizing, spent Friday night and most of Saturday in his Capitol Hill town house with a young woman who flew from Miami and met him." Three days later, on May 6, Washington Post reporter Paul Taylor asked the candidate point-blank at a New Hampshire news conference: "Have you ever committed adultery?" "I do not think that's a fair question," Hart replied. But two days later, following a tsunami of news coverage, he quit the race, excoriating a process that "reduces the press of this nation to hunters and presidential candidates to being hunted." By then a raucous debate over the propriety of reporting on candidates' personal lives had already begun.

Fiedler was pilloried by many of his colleagues for invading the candidate's personal terrain, but he says he has no regrets. "It all played out exactly the way it had to," says Fiedler, now a fellow at Harvard University's John F. Kennedy School of Government. "We were in a position, in the media, of playing the role of truth-testers." There was a significant gap, he says, between Hart's words and his actions, "and we thought we had an obligation to do something about it."

Taylor, now executive vice president of the Pew Research Center, a think tank based in Washington, says the Hart story "was a milestone in the evolution of our cultural norms, and our press norms. Today, for better or worse, there is more [scrutiny of candidates' private lives] than there used to be."

The Washington Post's Taylor also took considerable heat for crossing a threshold two decades ago. Columnist Edwin Yoder inveighed against what he called "totalitarian journalism"; other commentators warned that future generations of political reporters would be emboldened to probe candidates' private lives as a matter of routine. Taylor, also, says he had no qualms then and has none today.

"I'm delighted with the way I acted in the moment, and in my reflections thereafter," he says, referring to the question he put to Hart in New Hampshire. He says he felt he had had no choice; many sources had told him that Hart was reckless in his personal life, and even after the Herald published Fiedler and McGee's story, the candidate declared that he had always held himself "to a high standard of public and private conduct."

Hart, who declined to comment for this article, certainly did not intend this journalistic watershed to be his legacy. A lanky loner who kept his emotions to himself, he had determined in 1987 to seek the presidency on the issues. But even before he announced his candidacy, reporters had begun tapping their sources—including some ex-Hart advisers who had worked on his unsuccessful 1984 presidential bid—for off-the-record anecdotes about how he spent his free time. Indeed, Taylor and his Washington Post colleagues had debated how to cover the candidate more than a month before the Herald published its town house story.

"We kicked around the obvious questions," Taylor recalled in his 1990 book, See How They Run. "If a candidate for president is believed to be a womanizer, but there's no suggestion that his sexual activities have ever interfered with his public duties, is it even worth investigating, much less publishing? Is there a statute of limitations, or is screwing around in the past tense just as newsworthy as in the present? Is a series of one-night stands more reportable than a single long-term extramarital affair?" And, perhaps most important, "is Hart a special case, or if we begin looking into his mating habits, must we do the same with everyone else running for president?"

The mere fact of that newsroom debate was an indication that times were changing. A new generation of reporters, including a few women, was ascendant. And many men, having come of age amid the women's movement, were sensitized to the idea that women must be respected inside and outside of marriage and the belief that "the personal is political."

At the same time, thanks to party reforms crafted in 1969, candidates were no longer being anointed by bosses in smoke-filled rooms. Primary campaigns—and the press coverage of them—had become the arena in which candidates were vetted. And the lesson of Watergate and President Richard Nixon's resignation was that personal traits mattered—arguably more than a candidate's positions on issues.

As early as 1979, journalist Suzannah Lessard had articulated the new thinking in an article for the Washington Monthly: "A presidential candidate is asking for a much greater mandate from the citizenry, and so he must tolerate a much greater sacrifice of privacy," she wrote. With respect to philandering, "a politician's willingness to deceive in this matter does not encourage one about his honesty in others."

Many of those who recall the Hart imbroglio also recall the challenge he issued to the press in the form of a quotation that appeared in a profile about the candidate in the May 3 issue of the New York Times Magazine: "Follow me around. I don't care," he had told reporter E.J. Dionne Jr. "I'm serious. If anybody wants to put a tail on me, go ahead. They'd be very bored."

But by the time Fiedler read that, he was already on a plane out of Miami, heading for Hart's town house on Capitol Hill.

Fiedler's tipster had told him that Hart would be entertaining a woman at his town house the night of Friday, May 1. (Lee Hart, the candidate's wife then and now, would be at the couple's home in Colorado.) In subsequent calls, the tipster provided details. The intended guest was her friend, an attractive woman in her late 20s who spoke with a Southern accent. The caller refused to identify her friend by name or to provide her own but said the friend was scheduled to fly out of Miami that Friday.

She didn't supply a flight number, and Fiedler didn't know Hart's address in Washington. McGee, Fiedler's colleague, raced to the airport, guessing that the mystery woman would take a 5:30 p.m. Eastern Airlines flight to the capital. Fiedler, who stayed behind to work the phones, eventually learned Hart's Washington address from a Senate aide.

At the ticket counter McGee spied a woman who fit the tipster's description. He bought a ticket, shadowed her on the plane and watched as she was met in Washington—by another woman. He figured he had caught the wrong flight.

McGee then phoned a colleague in Washington, got Hart's address, took a cab to the neighborhood and stationed himself across the street. At 9:30 p.m., he saw the door swing open and Hart emerge—accompanied by the woman from the Eastern flight. McGee phoned Fiedler, who flew up the next morning (reading the New York Times Magazine profile en route), along with a photographer and an editor, and the surveillance continued.

After seeing the woman leave and reenter the town house on Saturday night, the Herald reporters confronted Hart outside. They later reported Hart's denials: "No one is staying in my house.... I have no personal relationship with the individual you are following." When the reporters asked to speak with the woman, Hart replied, "I don't have to produce anyone."

The Herald story, which ran the next morning, was widely read—and roundly criticized. The Capitol Hill surveillance had not been airtight, particularly during the wee hours of Saturday; the woman, later identified as Miami model-actress Donna Rice, might not have spent the night at the town house. At the same time, the Herald reporters were assailed by pundits and readers alike as peeping Toms.

But the story was taken seriously across town at the Washington Post, where Paul Taylor and his editors had already concluded that because Hart's private behavior raised broader questions about his judgment and honesty, it was fair game. That conclusion, and Hart's declaration that he held himself to a high moral standard, lay behind Taylor's question about adultery in New Hampshire.

Hart's refusal to answer it ("I'm not going to get into a theological definition of what constitutes adultery," he said) did nothing to make it go away. By then, he had come under fire for having vacationed with Rice in Bimini a month before, aboard a boat named, wouldn't you know, Monkey Business. Rice herself had volunteered this information to reporters on May 4. At no point during the fateful week after the Herald's story broke did Hart apologize to the electorate or concede any personal flaws; to the end, he insisted that he was the innocent victim of a censorious press.

Hart quit the race on May 8 (weeks before the National Enquirer published a photograph of him wearing a "Monkey Business Crew" T-shirt with Rice on his lap). His departure raised considerable alarm, even within the news business, that future political reporters would behave like vice detectives, scouring candidates' personal lives and clearing the field for only the most impeccably—or unrealistically—virtuous.

Nothing so drastic has happened. Most journalists generally shrink from that assignment.

At the same time, candidates are subjected to increased scrutiny. That is partly because politics has become more partisan over the past 20 years and partly because nontraditional media have moved into the political arena. "With bloggers and talk radio and the more partisan media in full flower, the norms of what's a story and what's not a story have been broadened," says Tom Rosenstiel, a former Los Angeles Times reporter who covered media and politics in the early 1990s and who now directs the Pew Project for Excellence in Journalism. "...It is a given now that everything is fair game."

In 1992, the supermarket tabloids—with help from Bill Clinton's opponents in Arkansas—reported allegations that the Democratic presidential candidate had had a long affair with a lounge singer named Gennifer Flowers. In 1998, as the House debated whether to impeach Clinton for lying about his indiscretions, House Speaker-elect Robert L. Livingston resigned after Hustler magazine publisher Larry Flynt got a tip that Livingston had conducted extramarital affairs. In 2004, Matt Drudge, the self-styled muckraker who runs drudgereport.com, trumpeted a rumor that presidential candidate John Kerry had committed "an alleged infidelity" with a Senate intern.

And yes, the mainstream press does probe private lives, when it feels they are relevant. A weeklong media frenzy followed Drudge's supposed Kerry scoop; no one found anything to corroborate it. At the beginning of the current campaign, there was copious coverage of GOP candidate Rudy Giuliani's marital difficulties. A New York Times report in February on the ties between presumptive Republican nominee John McCain and a female lobbyist was indeed widely criticized—but less for being inappropriate than for presenting the uncorroborated accusations of anonymous former McCain staffers.

For candidates, this is tricky terrain. Some try simply to put their actions in the most favorable light. Clinton went on CBS' "60 Minutes" to say that he and his wife had had "problems in our marriage," but that their bond was strong. Giuliani said only that he and his third wife, Judith, "love each other very much."

But campaigns are not, ultimately, about the candidates and the press; the voters have the last word. And for them, revelations of unsaintly behavior are not necessarily fatal. Despite his impeachment, Clinton left office in 2001 with a public approval rating of more than 60 percent for his job performance; Giuliani's marital history did not prevent him from polling strongly among Republicans on the eve of the primaries. Paul Taylor calls the phenomenon "the widening of the circle of acceptability."

Voters now "are increasingly willing to view these scandals on a case-by-case basis," Tom Rosenstiel says. "In terms of how we process this kind of information, we've all grown up a bit."

Dick Polman is the national political columnist at the Philadelphia Inquirer.