Nairobi — "Senator Obama, I am not President Bush. If you wanted to run against President Bush you would have stood for elections four years ago".

With that line early on in the final US presidential debate, Republican candidate John McCain underscored how aggressively he wanted to tackle what for him might have been the do-or-die event barely three weeks before voters troop to the polls.

Senator McCain was on the offensive throughout, throwing the heavy punches as Senator Obama, to continue the boxing analogy, parried, feinted, and replied with sharp jabs of his own.

A decisive knock-out

Aggression alone might well have given Mr McCain the edge, but that might have been of no consequence in a final round he needed to win by a decisive knock-out in order to make up the points deficit and revive his hopes for the White House.

The Arizona Senator went into the debate with new opinion polls showing him falling further behind his Illinois counterpart in both the national popular vote and the key states he needed to capture if he was to catch up on the delegates count.

It was clear well before the debate that Sen McCain would have no choice but to go on the offensive, even if it meant reviving the negative campaign he had signalled an end to just last week.

But he had no secret weapon, other than repeating the same charges that had failed to stick in the past week about Sen Obama's alleged association with 1960s radical Bill Ayers, and civil society group, ACORN, that is accused of massive fraud in voter registration.

It was a strategy, in any case, fraught with risk.

Senator McCain's previous dive into negative campaigning had backfired badly.

It had alienated uncommitted voters he badly needed to win, and also reinforced the impression, much to the Obama campaigns delight, that he was unable offer solutions to serious issues of the day such as the financial crisis and thus was resorting to mudslinging.

Ultimately it was Sen Obama who gave Sen McCain an entry point into the Bill Ayers and ACORN issues.

Prompted by moderator Bob Schiffer to talk about the negative aspect of the campaigns, both candidates defended themselves, and blamed each other, without going too much into specifics.

But at some point Senator Obama complained about accusations by McCain's running mate Sarah Palin that he associates with terrorists.

That was in reference to Mr Ayers who headed the radical Weather Underground group accused of a series of bombings, no casualties, during the period of protests against the Vietnam War.

Part of the exchange:

Obama: "When people suggest that I pal around with terrorists, then we're not talking about issues..."

McCain: "About Mr Ayers, I don't care about an old washed-up terrorist, but ... we need to know the full extent of that relationship. We need to know the full extent of Senator Obama's relationship with ACORN, which is now on the verge of maybe perpetrating one of the greatest frauds in voter history in this country, maybe destroying the fabric of democracy."

Obama: "Mr Ayers has become the centrepiece of Sen McCain's campaign over the last two or three weeks. This has been their primary focus. So let's get the record straight. Bill Ayers is a professor of education in Chicago.

"Forty years ago, when I was eight years old, he engaged in despicable acts with a radical domestic group. I have roundly condemned those acts. Ten years ago he served and I served on a school reform board that was funded by one of Ronald Reagan's former ambassadors and close friends, Mr Annenberg.

"Mr Ayers is not involved in my campaign. He has never been involved in this campaign. And he will not advise me in the White House.

"Now, with respect to ACORN, it had nothing to do with us. The only involvement I've had with ACORN was I represented them alongside the US Justice Department in making Illinois implement voter reforms. This has become such an important part of your campaign, Sen McCain, and that says more about your campaign than it says about me."

McCain: "The fact is Sen Obama chooses to associate with a guy who in 2001 said that he wished he had have bombed more, and he had a long association with him. All the facts need to be known about Sen Obama's relationship with them and with ACORN and the American people will make a judgment."

Was dominated

The debate, otherwise, was dominated by sharp disagreements on each others' policies on the specified themes - economic and domestic policies on issues such as healthcare, energy, education, taxation, and the financial sector crisis.

Both laid out their plans, but with very little in terms of detailed specifics, and they spent more time attacking the others' proposals than in advancing their own arguments.

Both generally agreed that the US economy is facing its worst crisis since the Great Depression, but they disagreed on the solutions and the cost, particularly in regard to taxation.

They also broadly agreed that there were problems in the quality and accessibility of education, runaway energy prices and the reliance on imported oil, lack of universal health insurance plan and many other issues.

But, again, they disagreed sharply on the solutions, with Mr McCain accusing Mr Obama of being a tax-and-spend liberal who wants to raise taxes and carry out "class warfare" on the wealthy.

In turn Mr Obama accused his rival of offering no workable solutions and offering only a continuation of the "failed" policies of President Bush.

But, the Republican candidate in fact continued with his recent strategy of trying to distance himself from the Bush administration, accusing it of presiding over massive failures, particularly on the economy.

Mr McCain tried hard to projected himself as the lifelong reformer who has bravely disagreed with the Bush policies over the last eight years.

In the end, however, he failed to deliver the killer punch, and if he does not find anything in the coming weeks that could destroy the Obama campaign, then he will have to rely on providence in the Democratic candidate making a major blunder.

Republican strategist Scott Reed said, adds Reuters: "That was McCain's best debate. He had Obama on the defense most of the evening and he closed with trust. Trust and judgment are what this thing is going to be all about."