Kerry, speaking at a midnight rally as Bush closed the GOP convention in New York with his acceptance speech, said the president was "unfit to lead this nation" because of the war in Iraq and his record on jobs, health care and energy prices.
He lashed out at the commander in chief and Vice President Dick Cheney for not serving in Vietnam during the war and for comments made during the convention about Kerry's fitness to occupy the Oval Office.
"I will not have my commitment to defend this country questioned by those who refused to serve when they could have and who misled America into Iraq," he told a crowd of thousands in Springfield.
Cheney and Sen. Zell Miller, D-Ga., led a chorus of Republicans who challenged Kerry's credentials to be commander in chief, arguing that although they respected his decorated Vietnam War service, Kerry's 20-year voting record in the Senate on national security issues made him unfit for the nation's top job.
Kerry faulted the president and Republicans for not talking about "real issues" - creating jobs, improving the economy, expanding access to health care and reducing gasoline prices.
"They did everything except talk about that" at the four-day convention, Kerry said. "We've had insults, we've had anger from Republicans. And I'll tell you why," Kerry said. "Because they can't come to you and talk to you about having created jobs since they've lost them. They can't come to you and talk to you about creating health care since 5 million Americans have lost it.
"Their own labor secretary talks about exporting jobs overseas," he said. "They can't talk about their record because it is a record of failure. And so all they do is attack."
After ceding much of the campaign spotlight to the Republicans and their convention this week, Kerry plunged back into retail politicking with a bus tour of Ohio, beginning in Dayton. It will take him east through Springfield, Newark, Akron and Steubenville by Saturday.
On Friday, he holds a "front porch" discussion and campaign rally in Newark.
Bush won Ohio by 3 percentage points in 2000 and the state is one of more than a dozen the two campaigns are fighting over. Kerry's trip to the Buckeye State is his 14th this year, while Bush has made nearly two dozen visits.
Besides Kerry, running mate, Sen. John Edwards, and spouses Teresa Heinz Kerry and Elizabeth Edwards will campaign Friday, also by bus, in the battlegrounds states of Wisconsin, Iowa and Michigan, respectively.
Kerry's campaign will go on the air in Ohio on Friday as part of a $50 million, two-month ad blitz, before expanding its ads to Florida, Iowa, New Mexico, Pennsylvania, New Hampshire and Wisconsin next week. Ads in 13 other states will come later in the fall.
Bush also is readying new post-convention ads, to begin airing Tuesday and laying out the elements of the second-term agenda he outlined in his speech.
Kerry said the GOP convention was tinged by "anger" and "distortion."
"For the past week, they attacked my patriotism and my fitness to serve as commander in chief," Kerry said. "I'm going to leave it up to the voters to decide whether five deferments makes someone more qualified than two tours of duty."
Bush served stateside in the Texas Air National Guard during Vietnam. Cheney, a former secretary of defense, received five deferments and did not serve in the military.
Edwards, introducing Kerry, said voters deserve a president who will fight for them.
Of Kerry, he said: "He is a fighter and you're about to see it."
By Darlene Superville