Democrat Barack Obama took to the airwaves with a half-hour paid television appeal in an effort to lock in his lead in the polls just six days before a presidential election that could alter the US political landscape.

The program, running on several major television networks simultaneously on Wednesday night, was an extraordinary last-minute effort to win over undecided voters, made possible by his huge financial advantage over Republican John McCain.

McCain derided the event as a "gauzy, feel-good commercial", paid for with broken promises.

He appeared as a guest on CNN's "Larry King Live" after charging earlier that Obama lacks "what it takes to protect America from terrorists".

In Obama's broadcast, the candidate was shown addressing large crowds on issues including health care, education and jobs, interspersed with the story of struggling American families, and interviews with Obama's family and colleagues.

Obama talked about how his mother died young of cancer. "I know what it's like to see a loved one suffer, not just because they are sick, but because of a broken health care system."

He also pledged to protect the US while seeking to wind down the war in Iraq.

"I will not be a perfect president," Obama said. "But I can promise you this - I will always tell you what I think and where I stand."

As the commercial ended, it cut to live shots of an Obama rally in Florida, where the candidate was shown with his running mate, vice-presidential candidate Joe Biden.

After Obama's broadcast, the candidate made his first joint campaign appearance with former President Bill Clinton, a fellow Democrat.

At the rally in Kissimmee, Florida, Clinton declared: "Folks, we can't fool with this. Our country is hanging in the balance. And we have so much promise and so much peril. This man should be our president."

"Barack Obama represents America's future, and you've got to be there for him next Tuesday," Clinton said to the cheers of a partisan crowd.

The broadcasts came as a new Associated Press-Gfk poll shows Obama well-positioned to dominate the state-by-state races that will decide the presidency.

With Obama poised to win all the traditionally Democratic states, the poll shows him leading McCain in four solidly Republican states - Ohio, Nevada, Colorado and Virginia. The candidates are tied in two others, North Carolina and Florida.

The poll numbers apparently reflect Obama's decision to pour money and effort into states that in previous elections could be relied on to back McCain.

In addition, Democrats are dominating early voting in six key states that President George W. Bush won four years ago, forcing McCain to play catch-up even before Election Day arrives next Tuesday.

Democrats outnumber Republicans among early voters in Iowa, North Carolina, Florida, Colorado, New Mexico and Nevada, according to statistics from election and party officials in those states. Bush won all six in 2004, and McCain needs to win most of them to claim the White House this year.

The beleaguered Republican, meanwhile, has been forced to commit his limited time and resources to shoring up his support in these traditional party strongholds.

The AP-GfK polls show Obama winning among early voters, favored on almost every issue and benefiting from the country's sour mood.

McCain faces a tight race even in his home state of Arizona, where the Cronkite-Eight poll showed him statistically tied with Obama. McCain led by only 46 to 44 percent, within the poll's margin of error of three percentage points.

"If you believe in miracles," said Republican consultant Joe Gaylord of Arlington, Virginia, "you still believe in McCain."

Obama leads in just about every national poll, but aides to McCain, a four-term Arizona senator, insist their internal surveys show victory is still within reach.

Questions:

1. Name three issues Democratic presidential nominee Barack Obama talked about in a half hour television ad.

2. How did Republican presidential nominee John McCain discredit Obama on CNN’s “Larry King Live”?

3. Obama is currently leading in which four traditionally Republican states?

Answers:

1. Healthcare, education, jobs, pulling out of Iraq.

2. He said Obama did not have what it takes to protect America from terrorists.

3. Ohio, Nevada, Colorado and Virginia.