Democrat Barack Obama hit White House rival John McCain with a prime-time TV onslaught as he vied to clinch victories in battleground states in the climactic run-up to next Tuesday's vote.

After his 30-minute appeal on national television late on Wednesday, which cost at least three million dollars to air, Obama held a midnight rally near Orlando with former president Bill Clinton in the latest burial of Democratic hatchets.

Obama beat Clinton's wife Hillary to the Democratic nomination, but the ex-president delivered a fulsome endorsement at his first joint campaign event with the party's 2008 champion in front of 35,000 supporters in Kissimmee.

"The presidential campaign is the greatest job interview in the world. And on Tuesday, you get to make the hire," Clinton said, contrasting the economic prosperity of his own 1990s tenure to the crisis now sweeping the nation.

"This is not a close question. If you make the decision based on who can best get us out of the ditch...I think it's clear the next president should be, and with your help will be, Senator Barack Obama," he said.

Obama is stepping up the pace on the final approach to the most consequential election in a generation, as the United States grapples with the financial hurricane and two wars in Iraq and Afghanistan.

The Democratic front-runner was to hit three states on Thursday, departing Florida after a morning rally for more events in the raging battlegrounds of Virginia and Missouri. McCain was conducting a bus tour of Ohio.

Pursuing his quest to be elected America's first black president, Obama ended his special broadcast with a live cut to the thumping climax of a rally attended by 20,000 supporters in Sunrise, Florida late on Wednesday.

The ad, which aired on three networks before the decisive World Series baseball game, featured patriotic tropes, intensely personal moments and stories of real Americans struggling to make ends meet.

The 47-year-old Democrat, promoted in the broadcast as a loving family man who overcame hardship to reach the pinnacle of politics, pledged to remake the American Dream for all and safeguard the nation from foreign threats.

"We've seen over the last eight years how decisions by a president can have a profound effect on the course of history -- and on American lives," he said intently to the camera.

"This election is a defining moment. The chance for our leaders to meet the demands of these challenging times and keep faith with our people."

Offensive McCain

McCain, 72, was to go on the offensive in Ohio on Thursday, the midwestern state that is pivotal to his chances of taking the White House.

The 72-year-old Arizona senator was to launch a two-day tour through the state on his Straight Talk Express bus, beginning with a rally in the somewhat appropriate location of a town called Defiance.

He denounced Obama's prime time appearance on Wednesday as he campaigned in Florida -- the biggest of all the battleground states where the November 4 election will be won and lost.

"When you're watching this gauzy, feel-good commercial, just remember that it was paid for with broken promises," he said, attacking Obama's decision to reverse course and opt out of public campaign financing.

The Arizona senator renewed his attacks on Obama's past links to 1960s radical William Ayers and lambasted his opponent's credentials to be commander-in-chief.

"With terrorists still plotting new strikes across the world, millions of innocent lives are still at stake, including American lives," he said.

"The question is whether this is a man who has what it takes to protect America from Osama bin Laden, al Qaida, and other grave threats in the world," McCain said. "And he has given you no reason to answer in the affirmative."

Whether the Republican's tactics are successful remain to be seen. Polls have repeatedly shown that the economy rather than national security remains the defining issue of the campaign.

A survey of toss-up states by CNN and Time had Obama expanding his lead in Colorado and holding steady margins in Florida and Virginia, which last voted for a Democratic White House hopeful all the way back in 1964.