"It will be different because we have the means and foundation with which to repel those attacks -- and we're not going to be passive about it," he said, after Obama rallied supporters in Portsmouth.

Asked to elaborate, Axelrod declined to discuss any specific response strategy, but did quibble with a reporter who suggested that Obama would be reneging on his promise to run a different kind of campaign if he launches an aggressive counter-attack.

"Your assumption is that the only way to respond is to do what they're doing -- to be gratuitous about it," he said.

He also predicted a backlash against any Clinton attacks: "When (negativity) begins to define your campaign, it's one more way in which you have a very difficult time standing up and saying that you're the candidate of change."