You would have thought that if the issue of who served under fire during the Vietnam War became a big deal at this point in the presidential campaign, it would be a major advantage to John Kerry.

After all, there is no dispute that Kerry served in Vietnam's combat zones while both President Bush and Vice President Cheney avoided the war. Bush served stateside in the National Guard (it's still not clear how much of his duty time he missed) and Cheney avoided the military altogether. The hawkish veep has explained blithely, "I had other priorities in the '60s than military service."

Republicans insisted that military service was an important criterion for leadership when Bill Clinton ran against the elder George Bush and former senator Bob Dole, war veterans both. But the Republican attack maestros were never as interested in service as they were in taking and holding power. So now it's Bush supporters, through a front group, attacking the war veteran -- much as they attacked Vietnam hero John McCain during the Republican primaries four years ago when McCain dared to challenge Bush.

This episode is a great test of how politics work in our country. It is, first, a test of George W. Bush.

Bush claims that his highest priority is uniting the country in the war against terrorism. A president who would be a uniter and not a divider knows that cheap-shot politics can only further rend our nation and weaken his own ability to lead.

Yesterday Bush offered what you might call a nuanced response to the controversy over the anti-Kerry ads. While praising Kerry's service, Bush issued only a blanket condemnation of all ads by outside groups. What Bush really needs to do is tell the inappropriately named Swift Boat Veterans for Truth to stop smearing Kerry's service record and urge his big money contributors to stop bankrolling the distortions.

This is also a test for the media. We see here a fascinating and ugly development in the politics of annihilation. A supposedly outside group raises money from close Bush supporters, staffs itself with political operatives close to Bush and the Republicans, and then puts up several hundred thousand dollars worth of television ads. This is, as one operative with years of experience in Republican campaigns put it, "a professional hit." Suddenly, questions about Kerry's service that were asked and answered months ago become big news again.

To their credit, several news organizations -- the New York Times, Chicago Tribune and The Post among them -- have run reports exposing the distortions, inconsistencies and fabrications of the anti-Kerry crowd, and the links between this operation and the Bush machine.

But this hasn't stopped the run of unproven innuendo. Even highly respected Republicans have jumped in. "There's got to be some truth to these charges," Dole, a true war hero, said on CNN.

Alas, this is the classic course a smear campaign takes. A group throws up accusations that, when subjected to scrutiny, prove to be full of holes. Supporters of the attack campaign say that, well, those charges may not pan out, but there must be something here. Let's just keep attacking.

The media have to do more than "he said/he said" reporting. If the charges don't hold up, they don't hold up. And, yes, now that John Kerry's life during his twenties has been put at the heart of this campaign just over two months from Election Day, the media owe the country a comparable review of what Bush was doing at the same time and the same age.

If all the stories about what Kerry did in Vietnam are not balanced by serious scrutiny of Bush in the Vietnam years, the media will be capitulating to a right-wing smear campaign. Surely our nation's editors and producers don't want to send a signal that all you have to do to set the media's agenda is spend a half-million bucks on television ads.

This is also a test of John McCain. When he ran against Bush four years ago, McCain was smeared mercilessly. When McCain protested to Bush about the attacks at one of their debates during the 2000 primaries, Bush brushed him off. "John," Bush said, "it's politics."

McCain snapped back, "George, everything isn't politics."

McCain was right, and when he returns to the United States from a trip to Europe this week, he should stand up for that principle by suspending his campaigning for Bush's reelection until the smears against Kerry's Vietnam record stop. More than anyone, McCain is the person to make the case that slaughterhouse politics is particularly ill-suited to this moment in our history.