Reacting to the turmoil on Wall Street, the Dow dropped some 300 points.
"Our economy, I believe, still, the fundamentals of our economy are strong, but these are very, very difficult times, so I promise you: We will never put America in this position again. We will clean up Wall Street," McCain said.
He added: "The McCain-Palin administration will replace an outdated, patchwork quilt of regulatory oversight and bring transparency and accountability to Wall Street. We will have transparency and accountability and we will reform the regulatory bodies of government."
In a brief interview, McCain was questioned about the economic woes under eight years of President Bush and six years of GOP control of Congress.
"I think it's a failure of government and I think it's a failure of regulatory agencies," McCain told reporters.
"I would point out that the Democrats have been in control of Congress for the last two years - both houses, so I think there's plenty of blame to go around."
The GOP nominee underscored his message with a new campaign television commercial that seemed to contradict his rosier assessment of the country's economic health.
It is titled, "Crisis" and said, "Our economy in crisis. Only proven reformers John McCain and Sarah Palin can fix it. Tougher rules on Wall Street to protect your life savings. No special interest giveaways. Lower taxes to create new jobs. Offshore drilling to reduce gas prices."
The ad will run nationally on cable and network television but will not be part of McCain's more expensive and intensely targeted rotation of ads in battleground states, the campaign said. McCain has been spending about $600,000 a week on national ads. The Obama campaign ridiculed the commercial.
"Today of all days, John McCain's stubborn insistence that the 'fundamentals of the economy are strong' shows that he is disturbingly out of touch with what's going in the lives of ordinary Americans," spokesman Bill Burton said in a statement.
Over the weekend, advisers both to McCain and Democratic rival Barack Obama said they did not favor a government bailout of Lehman Brothers like that previously provided to Fannie Mae and Freddie Mac. The government also help engineer the recent sale of Bear Stearns Cos. to J.P. Morgan & Co.
During his speech, McCain reiterated that position, saying, "We believe the time has come and gone that taxpayers should be viewed as the solution to problems not of their making."
The financial turmoil threatened to overshadow two events on McCain's schedule not seen in weeks: his solo campaign rally and a town hall meeting.
The Republican presidential contender visited the city where he once commanded a Navy squadron for his first individual rally since announcing Sarah Palin as his running mate over two weeks ago. Then he was flying to Orlando to take questions from an audience for the first time since a session in Las Cruces, N.M., before he accepted his party's nomination at the Republican National Convention.
Aides hoped for a sizable turnout for the Jacksonville rally, a special wish after Palin drew thousands Saturday in Carson City, Nev.
McCain was greeted by a crowd of several thousand who filled less than a quarter of the Jacksonville Veterans Memorial Arena.
In a personal remark rarely made on the trail, he thanked the audience for caring for his first wife, Carol, and their three children during the 5 1/2 years he was a Vietnam prisoner of war.
"I hope you know that in the years I was away in prison, the people of Orange Park, Fla., took care of my wife and family," McCain said. "The people of Jacksonville opened their hearts to my family. For that, I will be extremely grateful. My children had about 50,000 parents while I was gone and I'm very grateful."
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