Democratic presidential nominee Senator John Kerry has strongly attacked the Iraq war and drawn an angry response from US President George W. Bush.
Marking Labour Day, the traditional kickoff for the presidential campaign season, the two candidates held rallies in the battleground states of Missouri, Pennsylvania, West Virginia and Ohio.
Mr Kerry, trailing by double digits in some national polls, tried to focus on domestic issues at a neighbourhood meeting in Canonsburg, Pennsylvania.
But members of the audience raised Iraq, and after months of off-and-on criticism of the war, Mr Kerry seized the opening. He called the invasion "the wrong war in the wrong place at the wrong time," and said his goal was to withdraw US troops in a first White House term.
Mr Kerry later issued a statement calling Iraq a "quagmire" created by Mr Bush's "wrongheaded, go-it-alone" policy.
Mr Bush, at a rally in Missouri, accused the Massachusetts senator of vacillating on Iraq after bringing in new advisers. "My opponent woke up this morning with new campaign advisers and yet another new position," Mr Bush said. "Suddenly he's against it [the war] again.
"No matter how many times Senator Kerry changes his mind, it was right for America then and it's right for America now," he told the crowd.
With scarcely two months until the November 2nd election, some senior Democrats have advised Mr Kerry to focus on jobs and the economy as he tries to reinvigorate his campaign.
Polls show Mr Bush's popularity with voters is particularly strong on Iraq and issues of national security, while Mr Kerry poses more of a challenge on health care, the economy and jobs, generally the centrepiece of Labour Day campaigning.