Referring to the Senate investigation which found that the principal claims justifying the invasion of Iraq were fundamentally wrong and the result of a "global intelligence failure", Mr Kerry argued that Mr Bush's record had fed cynicism and mistrust of government.
"They were wrong and soldiers lost their lives because they were wrong. And America's paying billions of dollars because they were wrong. And allies are not with us because they were wrong," Mr Kerry told the New York Times in one of several interviews with his new running mate, John Edwards, published yesterday.
Mr Edwards added: "My view is that what George Bush has done in Iraq, both in the lead-up to the war and more importantly his planning for winning the peace, has cost America dearly and cost the possibility of success dearly."
As senators, Mr Edwards and Mr Kerry last year voted for the resolution authorising Mr Bush to go to war, but both declined to say whether they would change their votes if they had known then what they know now.
Asked whether he believed the war on Iraq had made the country more vulnerable to terrorist attack, Mr Kerry said: "I believe that the overall conduct of this administration's foreign policy ... has not made America as safe as we ought to be, given the options available to us in the aftermath of 9/11."
In an interview with the Washington Post, Mr Kerry slammed the administration for acting in a dishonest manner, that transgressed a value Americans hold dear.
"The value of truth is one of the most central values in America, and this administration has violated it," he said. "Their values system is distorted and not based on truth."
Meanwhile, Democrats successfully avoided a platform fight at this month's Boston convention over the war, where supporters of the leftwing candidate, Dennis Kucinich, had planned to submit a motion calling for the rapid withdrawal of US troops from Iraq. Polls show that a majority of Democrats would support this position by 56% to 38%, but the Kerry campaign feared it might alienate moderates and expose divisions within the party.
Republicans seized on Mr Kerry's statements and his record to reiterate one of their central claims that he is an opportunist who keeps shifting his stance to please his audience. "Senator Kerry's position on the war has changed on an almost weekly basis," said Steve Schmidt, a Bush campaign spokesman.
The interviews ended a week of tightly choreographed media appearances for the Democratic team since Mr Kerry announced Mr Edwards as his running mate on Tuesday. With the polls showing a tight but volatile race, Republican campaigners are expecting the Democrats to surge ahead into early August, following their convention at the end of this month.
"John Kerry should have a lead of more than 15 points coming out of his convention," wrote President Bush's chief strategist, Matthew Dowd, in an internal memo.
· The Republican convention takes place in New York at the end of August.