Michelle Obama took her husband's place on the campaign trail [Reuters]

McCain told a noisy rally in Denver, Colorado on Friday, that "the answer to a slowing economy is not higher taxes, but that is exactly what is going to happen when the Democrats have total control in Washington."

Obama has left his campaign to visit his sick grandmother in Hawaii, and Michelle Obama, his wife, spoke on his behalf in the key swing state of Ohio.

But McCain again argued that Obama would raise taxes on small businesses.

He cited Obama's recent comment to an Ohio man, Joe Wurzelbacher, also known as "Joe the Plumber," that he wanted to "spread the wealth around."

"My opponent's massive new tax increase is exactly the wrong approach in an economic slowdown," he said.

However, Obama told ABC News from Hawaii that he did not regret making the remark.

"Not at all," the Illinois senator said.

"For us to want to continue to give tax breaks to big corporations and the wealthiest, instead of the middle class that are desperately in need of some help right now, would not only be bad for the families, it would be bad as the economy as a whole."

Poll battle

The Illinois senator has maintained a double digit lead in national polls, although McCain appeared to have made a small gains in one poll released on Friday.

Obama leads McCain by 51 per cent to 41 percent among likely US voters in the latest three-day Reuters/C-SPAN/Zogby tracking poll, although Obama had held a 12-point lead on Thursday.

"McCain stopped the bleeding a little bit but he still has a long way to go," said John Zogby of Zogby International, an opinion poll company.

Opinion polls in key battleground states have also shown Obama maintaining a lead over his Republican rival.

Obama was also boosted by the endorsement of another former senior Bush administration official on Thursday.

Scott McClellan, the former White House press secretary, said on Thursday he wanted to support the candidate with the best chance of changing the way Washington - the political heart of the US - works and of getting things done.

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