Excellent editorial in The New Republic. Segments:

Just how dishonest must a smear campaign be for American journalists to say so plainly or, better yet, to ignore altogether? That's the only real question still unanswered in the controversy sparked by the group Swift Boat Veterans for Truth over John Kerry's service in Vietnam--although even to use the word "controversy" affords the issue's protagonists too much dignity. The veterans featured in the organization's TV ad claim to have "served with Kerry," but none actually served on the same boat. (Yes, we've been reduced to arguing over what the definition of "with" is.) Several of the charges are based on recollections by veterans who, years earlier, had praised Kerry for the very same actions.The accusation that Kerry faked one of his injuries turns out to come from a thirdhand account. Most important of all, the surviving crewmembers from Kerry's boat--as well as Navy records--back Kerry's version of events.
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The effect was to spread lies rather than scrutinize them, in a precise perversion of journalism's supposed purpose. More than half of the respondents to a survey by the Annenberg Public Policy Center said they had seen or heard of the Swift Boat ad, which initially ran in only three swing states. And the polling firm HCD Research found that 27 percent of independent voters who saw the ad and "who [had] planned to vote for Kerry or leaned pro-Kerry" were "no longer sure they'd back" him.

Journalists, in short, became accomplices to fraud. And they should have known better. In 2000, Bush and his right-wing allies learned that the way to win political arguments is to launch rhetorical attacks based only loosely--if at all--on the facts and then depend on reporters to spread them as credible perspectives on the truth. And, ever since, this White House has conducted its business the very same way, shamelessly peddling lies about everything from budget projections to weapons of mass destruction without the slightest fear of retribution.