My first lesson about journalists’ vision of their responsibilities came in a congressional primary 20 years ago. Candidates had to secure support from convention delegates to get on the ballot. Each side attempted to demonstrate momentum by releasing lists of delegates committed to them. Some names appeared on both lists, and the great metropolitan newspaper covering the story duly reported that a number of delegates were claimed by both campaigns.

Frustrated by the dissembling of our opponent, I asked the reporter why he did not simply call the individuals in dispute and ask them whom they intended to support. His answer shocked me.

“My job,” he responded, “is not to find the truth but to report the news. The news is that both campaigns claim the same delegates.”

At first I put it down to lazy journalism, but I discovered since that different reporters bring somewhat different job descriptions to their writing. Some see themselves as reporters of events, others as arbiters of truth.

This and other principles of journalistic behavior were on display during 2004’s Swift boat controversy, now generating some media replay. While there were differences inside the campaign on how to respond, as one who favored an earlier, more vigorous counter it must be said that the campaign was raising doubts about the Swift boat attackers long before their ad debuted in three states.

During the two weeks after the ad, a variety of voices were raised in support of Kerry, ranging from Jim Rassmann, the soldier he had saved, to crewmates present at the engagements, but the press treated it largely as a he-said, she-said story. Like my antagonist 20 years earlier, many journalists were unwilling to play referee, testing the validity of competing claims, contenting themselves to merely report what was being said. Eventually, acting mostly on leads provided by campaign staff, major newspapers laid out the case against the Swift boat attackers in devastating detail.

It is difficult to know exactly what will trigger a media avalanche like this. An AP spokesman claimed they gave short shrift to the ad until “the story exploded when John McCain weighed in,” calling the ad “dishonest and dishonorable.” So, if the wire service is to be believed, their 78 stories in August were occasioned not by the Swift boat attack itself but by McCain’s counterattack the following day.

Voters paid attention because stories are more compelling than facts. The attacks were a story — a salacious one at that, involving a suddenly very important person about whom people knew little. The truths were just a series of facts, hard to organize into a coherent whole.

Moreover, John Kerry, not his attackers, was the object of journalistic interest. After one of Kerry’s chief accusers, John O’Neill, told ABC that Swift boats never ventured into Cambodia, a campaign researcher unearthed a tape from the Nixon library wherein O’Neill talked about his own Swift boat trips to Cambodia. The man either lied to the president in a private Oval Office meeting or lied on national TV. It barely caused a ripple.

Below-the-radar shout fests, where truth’s value is often not even a minor concern, can drive the broader media agenda. Indeed that is frequently the response of mainstream media: “We don’t believe the story, but it is having an impact so we cover it,” thereby increasing its impact.

Critics from the right and left are quick to offer media conspiracy theories. There is no conspiracy. Reporters and the institutions for which they work just have their own imperatives. Delivering the news is one. Delivering the truth is not always.

Mellman is president of The Mellman Group and has worked for Democratic candidates and causes since 1982, including Sen. John Kerry (D-Mass.) in 2004.