The kumbaya party George W. Bush has united the Democrats. Now it's up to John Kerry and John Edwards to translate that unity into victory. BY DAN KENNEDY

AMONG THE EVER-shifting blocs and factions that make up the Democratic Party, unity is an elusive and fleeting thing, more a goal than a destination, a theory rather than reality. So perhaps the thousands of Democrats gathered in Boston this week should pay tribute to the man who brought them together.

No, not John Kerry. Unlike Bill Clinton, who obliterated party divisions through the sheer force of his personality and his prodigious political gifts, the Massachusetts senator inspires respect, not passion. Rather, the Democrats are joining as one this week because of George W. Bush, reviled among the party faithful as surely the worst president since Richard Nixon, if not James Buchanan. Few speechmakers have resisted the urge to observe that Bush — true to his 2000 campaign promise — has, for the Democrats at least, been a uniter, not a divider.

On the left, you hear it from Fahrenheit 9/11 director Michael Moore, telling a crowd of young Howard Dean supporters on Tuesday to vote and work for Kerry rather than Ralph Nader, and never mind that Kerry voted for the war in Iraq. "One thing about Kerry," Moore thunders. "He will not invade a country the way George W. Bush did." You hear it from Arianna Huffington, speaking at a Sunday tribute to the late senator Paul Wellstone, telling the progressives who have packed the Old West Church, "When your house is on fire, it’s not the time for remodeling." You even hear it from far-left Boston city councilor Chuck Turner, who, at the Wellstone event, pronounces himself a Kerry supporter even though he thinks the senator "isn’t prepared mentally, emotionally, spiritually to be the president we need."

You hear it from the party’s moderate wing as well. Following an event on Tuesday at Radius, a stylish restaurant in the Financial District, Simon Rosenberg — president and founder of the centrist New Democrat Network, an outgrowth of the better-known Democratic Leadership Council — told me, "I think all wings of the party are flying this week. Moderates and liberals are speaking with a single voice because I think we really are unified. There is no evidence of left-right fighting in the Democratic Party right now. I credit John Kerry. And George Bush."

Yet there are limits to the kumbaya approach, limits that could be exposed and exploited by the Republicans’ relentlessly negative attack machine. Rosenberg, for instance, insists that it is possible to appeal both to the Democratic base of liberal voters and to swing voters who consider themselves moderate. So I asked him — coming up with the most crudely simplistic example I could think of — how to reconcile liberal opposition to the death penalty with the more mixed view held by those in the middle. Rosenberg’s solution: change the subject. "It’s not a zero-sum game, because undecided voters do not make up their minds on a single issue," he said, explaining that the Democrats should focus on three broad areas: security, the economy, and health care. Sound advice, perhaps, but it’s doubtful that Karl Rove will play along.

Which is why much is riding on Kerry’s prime-time speech on Thursday, the last night of the convention. An oft-repeated observation this week is that polling data show as many as 40 percent of potential voters know very little about him, even if they have expressed a strong interest in voting for him. The proverbial most-important-speech-of-his-life is the best opportunity he’ll have to introduce himself to the American people, to show some warmth and strength, and to reach out to his party’s moderate and liberal wings while simultaneously framing an appeal to independents.

"He hasn’t really made the sale yet, which puts tremendous pressure on Thursday night. He’s got to be really good," says Robert Kuttner, co-editor of the liberal American Prospect magazine and a syndicated columnist.

The conventional wisdom is that the country remains as evenly divided as it was four years ago, when the contest between Bush and Al Gore ended in a virtual dead heat. Thus, the easy call is to predict that the 2004 campaign will yield a narrow win for Kerry or Bush. But with Bush’s job-approval ratings stuck below 50 percent, and with Democratic-leaning organizations registering thousands of new voters, there is a sense that Kerry might be able to win decisively, and return one or both branches of Congress to Democratic control as well.

"We are clearly on the verge of a major Democratic victory in the presidency, in the Senate, and in the House," Congressman Barney Frank shouted into the microphone during a party for the Massachusetts congressional delegation on Monday at the Moakley Federal Courthouse. (Frank also warned that if the Democrats do win, "we will have inherited a very difficult situation," with "no friends and no money.")

Can Kerry take advantage of the opportunity that has been handed to him? Bill Clinton’s rousing speech on Monday night suggests what a long way Kerry has to go. Clinton oozed dynamism and charisma, masterfully talking about his own new wealth as a way to criticize Bush’s tax cuts for the wealthy, and about his own (and Bush’s and Dick Cheney’s) efforts to stay out of Vietnam as a way to praise Kerry’s military heroism.

Kerry couldn’t have asked for a better tribute. But on Thursday — and for the three months remaining in this seemingly endless presidential campaign — he’s got to do as well on his own.