He had ruffled the feathers of his former colleagues with the publication of What Happened, a book that was critical of Bush and exposed some of the inner workings of the administration.

Candidates spar

The news came after the US presidential candidates attacked each other once again on economic issues as they continued to campaign across key battleground states.

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McCain told voters in Florida that Obama's plan to raise taxes on small businesses making more than $250,000 would "kill jobs" and "comes at the worst possible time for America".

The McCain campaign also released a new advertisement using "Joe the Plumber", the Ohio plumber who questioned Obama over his tax plans earlier this month.

Trailing in opinion polls both nationally and in many key states, McCain is facing a difficult path to victory and finds himself racing to defend states that have voted Republican in recent elections.

'International crisis'

However, Al Jazeera's Rosiland Jordan, who has been following the McCain campaign, said the message based around "Joe the Plumber" was resonating, at least among his supporters, who cheered every time the name was mentioned.

The Arizona senator's latest campaign advertisement features a number of Americans all saying "I am Joe the Plumber too".

"Senator Obama is more interested in controlling who gets your piece of pie than he is in growing the pie," McCain told a cheering crowd at an Ormond Beach timber yard.

"He's more concerned about using taxes to spread the wealth than creating a tax plan that creates jobs and grows our economy," he said.

McCain also again used an assertion by Joe Biden, Obama's running-mate that, like John F Kennedy, Obama would be tested with an international crisis within six months of taking office.

"Senator Obama tried to explain away this by saying his running mate sometimes engages in 'rhetorical flourishes'. Really? Really?" he said.

Bush link

Obama says his tax plan would give a tax cut to 95 per cent of Americans.

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The Illinois senator gave his last campaign speech in Indiana on Thursday before leaving the campaign for two days to go to Hawaii to be with his gravely ill grandmother.

Obama said the US could not afford a president McCain who "thinks the economic policies of George W Bush are just right for America".

"He made kind of a strange argument that the best way to stop companies from shipping jobs overseas is to give more tax cuts to companies that are shipping jobs overseas," Obama said of his opponent.

"More tax cuts for job outsourcers. That's what Senator McCain proposed as his answer to outsourcing."

With less than two weeks before the election, Obama leads McCain 52 per cent to 40 per cent among likely voters in the latest three-day tracking poll by Reuters/C-SPAN/Zogby.

However, an Associated Press poll released on Wednesday put the gap between the two at just one per cent with Obama on 44 per cent and McCain 43.