“There’s no question John Edwards is different now than he was in 2004,” said Peter Scher, whom Mr. Kerry recruited to run Mr. Edwards’s vice-presidential campaign. “There’s a great deal more confidence in his own instincts and his own judgment. You see much less reliance on consultants and pollsters and media advisers, and more of a willingness to say what he believes and let the chips fall where they may.”

Image John Kerry and John Edwards, running mates but never really friends, ended 2004 in recrimination and regrets. Credit... Ting-Li Wang/The New York Times

Kerry loyalists, meanwhile, seethe as they watch his new aggressiveness. Stephanie Cutter, who was Mr. Kerry’s communications director, said, “A lot of what I’m seeing now, I wish I’d seen in 2004.”

Mr. Edwards defends his change in tone, calling it the result of “a maturing process.”

“I believe that presidential candidates actually have a responsibility to point out substantive differences, to point out perspectives that are different,” he said in an interview. “I’m totally comfortable doing it.”

Unlikely Pair

John Edwards began campaigning to be John Kerry’s running mate as soon as his own presidential run collapsed when he failed to win any of the Super Tuesday primaries in March 2004. He appeared at rallies for Mr. Kerry. He dispatched emissaries to party officials and Kerry aides, promising that he could raise $20 million and help win his home state, North Carolina, and others the campaign hoped to turn to blue from red. And, as an experienced trial lawyer, he could take on Mr. Cheney.

Mr. Kerry remained hesitant. He had not really known Mr. Edwards in the Senate, and on the primary trail, small resentments had built up. Mr. Kerry wondered why Mr. Edwards thought he could be president before even finishing his first Senate term; Mr. Edwards thought Mr. Kerry did not know how to talk to rural and Southern voters and could not win without them. He bristled at Mr. Kerry’s presumption: when Mr. Kerry said in a debate how he would take on President Bush, Mr. Edwards rebuked him, “Not so fast, John Kerry.”

The two men could hardly have been more different. Mr. Kerry was the craggy Brahmin raised in privilege, Mr. Edwards, smiling, Southern and self-made. Mr. Kerry had all the gravitas Mr. Edwards was often accused of lacking, but Mr. Edwards charmed colleagues and connected with voters in a way that Mr. Kerry could only envy.

Mr. Kerry had spent a career in the Senate, where success depends on accommodating all sides of an issue; he called friends ceaselessly to solicit different points of view until aides seized his cellphone. Mr. Edwards had built his career by choosing a side and not relenting; he was well known for turning down big settlement offers because he was confident he could win his case.