If John Kerry is elected president, his speech accepting the Democratic nomination will be only part of the story. At least as important will be the antidote that Democrats brought to market at their convention this week to combat three decades of Republican attacks around social issues, "values" questions and patriotism.

Since the late 1960s, the Republicans have often cast Democrats as living outside the American "mainstream," supporting exotic values popular in places such as San Francisco and, yes, here in Massachusetts, home to both Kerry and Edward M. Kennedy.

Sometimes directly and often indirectly, Republicans linked Democrats to flag burning, libertine personal values, indifference to family life and a preference for self-indulgence over hard work. In 1972 Richard Nixon's campaign came up with a snappy formula, deriding Democrats as the party of "acid, amnesty and abortion," amnesty referring to forgiveness of draft resisters. A similar line of attack helped create the Reagan Democrats of the 1980s, elected this president's father in 1988 and is being used relentlessly by the current president's campaign.

Bill Clinton had some success beating back the charges in the 1990s, largely by declaring that Democrats favored the same values as Republicans. But at this year's convention, the Democrats -- including, interestingly, Clinton himself -- scrapped the defensive approach and went on offense.

Thus emerged a major theme of this fall's campaign: that Republicans are a party of dividers who can win only by setting one group of Americans against another.

Clinton established the theme in his speech on the convention's first night. "They need a divided America," Clinton said of Republicans. "We don't." Clinton saw the country as favoring Democratic solutions on the practical issues of education, child care, job creation and tax fairness. Republicans thus need to bury such issues beneath controversies over gay rights, abortion and race.

A stout rejection of that sort of politics lay at the heart of Illinois state Sen. Barack Obama's remarkable keynote address. "There's not a liberal America and a conservative America, there is the United States of America," Obama declared and then riffed on the division of the country between red, Republican states and blue, Democratic states. "We coach Little League in the blue states and yes, we've got some gay friends in the red states."

And vice presidential nominee John Edwards kept up the barrage, contrasting "the tired, old, hateful, negative politics of the past" with "the politics of hope, the politics of what's possible."

Attacking divisiveness could yield multiple dividends in the fall. Having laid down their argument, Democrats can respond to Republican attacks with a breezy, Reaganesque "there they go again." The Kerry campaign expects President Bush to continue his withering assault on the Democratic candidate. By placing every Republican attack in the context of "old, hateful, negative politics," Democrats hope to raise the cost to Republicans of running the campaign that Bush's advisers will need to run if the president's popularity ratings don't improve.

But Democrats see the call for national unity as providing them an even larger benefit in the wake of the attacks of Sept. 11, 2001. Rep. John Spratt of South Carolina argued that Americans felt "a sense of common purpose" after the terrorist assaults, are disappointed that the feeling of solidarity has ebbed and yearn to bring it back. Sen. Kent Conrad of North Dakota linked Bush directly to the loss of national cohesiveness. "Bush said he was going to be a uniter, not a divider," Conrad said, "and now it turns out that he's divided us at the very moment when we most need to be united."

It's commonly said that this convention was designed to "move the Democrats to the center." Actually, it was a convention designed to move the center toward the Democrats. Throughout the convention, the large screen above the podium showcased stories of Republicans who are now for Kerry and former Republicans who are now Democrats.

Since when has a Democratic convention featured so many retired generals? Since when have Democrats spoken so much about the needs of veterans, reservists and the nation's military personnel? Since when have Democrats argued so explicitly and vociferously that their approach to national security is both tougher and smarter than the Republican approach?

This was the convention of a party that thinks discontent with President Bush could move the political argument in a different direction and new constituencies the Democrats' way. A party so accustomed to beating back the attacks of others has made clear that this time it is taking the fight to its adversary.