But David Axelrod, chief strategist to Mr. Obama, argues that any Democratic nominee will be subject to the same withering attacks on values and character.

Image Michael S. Dukakis, right, and Lloyd Bentsen in 1988. Credit... Elise Amendola/Associated Press

“The question,” Mr. Axelrod said, “is whether given the abysmal state of our economy, given the war, given all the challenges that people sense we face that have led George Bush to have the lowest rating ever, do you believe that voters are going to be distracted from the fundamental need for change? I think the answer to that is no.”

In fact, as Mr. Axelrod suggests, these are very different times.

Twenty years ago, the nation was in an era of comparative peace and prosperity; a sense of crisis did not hang over the election. Today, with the war in Iraq in its sixth year and the economy stumbling, more than 8 in 10 Americans say the country is on the wrong track. A new generation of voters have entered the electorate, who may not be as susceptible to values issues.

In such a climate, it would presumably be far more difficult than in 1988 to keep the campaign focused on symbolic, values-related issues, or matters of personality.

There are differences, as well, in the political skills of the candidates then and today: Mr. Obama rose to national prominence largely on the basis of his oratorical skills, and has never been accused of lacking vision; Mr. Dukakis based his campaign on a prosaic promise of managerial competence and “good jobs at good wages.”

And yet, some veterans of past Democratic campaigns say, there are similarities, as well.

Even with so many big issues at stake this time around, the race between Mr. Obama and Mrs. Clinton has often been focused on questions of values, background and character  witness the recent fixation on Mr. Obama’s ties to the Rev. Jeremiah A. Wright Jr., or the continued unfounded rumors that Mr. Obama is a Muslim.

Like Mr. Dukakis in 1988, Mr. Obama is relatively new to the national scene, and thus vulnerable to being defined by Republican attacks. And like Mr. Dukakis, Mr. Obama lacks experience with the politics of wedge issues on a national stage.