As Mr. Biden eventually acknowledged, that did not work as he had hoped.
“It was a mistake to assume the president would use the authority we gave him properly,” he said on NBC’s “Meet the Press” in 2005.
But on the campaign trail this election cycle, he has suggested he opposed the war and Mr. Bush’s conduct from the beginning, claims that do not match the historical record.
“Immediately, the moment it started, I came out against the war at that moment,” he told NPR in an interview in September. His campaign later said he had misspoken, according to a fact check from The Washington Post. At a campaign stop in Des Moines this month, Mr. Biden said, “The president then went ahead with ‘shock and awe,’ and right after that, and from the very moment he did that, right after that, I opposed what he was doing,” a misleading assertion at best, according to an assessment from CNN.
Mr. Biden did ultimately become a vocal opponent of the Bush administration’s stewardship of the war, and went on to serve as vice president to Barack Obama, a critic of the conflict. The war took a personal toll when his elder son, Beau Biden, deployed to Iraq in 2008 with the Delaware Army National Guard. Beau Biden died in 2015 from brain cancer, and his father has discussed the possibility of a link between the illness and exposure to pits of burning waste on military bases.
Ms. Boxer attended a fund-raiser for Mr. Biden last week, though she said she was not yet formally endorsing him, and spoke warmly about her former Foreign Relations Committee colleague in an interview. She emphasized his record and all he had done in the nearly two decades since they clashed on Iraq.
“They fought very hard to get us on board and we fought very hard to get them to stop,” Ms. Boxer said. “Once he saw that it was a mistake, he really stepped up to the plate to try and come up with a way out of this war.”
Ahead of that 2002 vote, Mr. Biden stood on the Senate floor to explain his support for the war authorization. He followed Senator Hillary Clinton of New York — who in her later presidential campaigns also faced scrutiny over her Iraq war vote — and spoke for about an hour.