John McCain tonight faces Barack Obama for a second presidential debate in which he will seek to reverse a recent tide flowing in the Democrat's direction.

The Republican nominee, after spending several days aggressively attacking his rival's character, truthfulness and background as a typical "Chicago politician" has promised viewers will see him "take the gloves off".

Mr Obama hopes to keep voters focused firmly on the economy, an issue that has helped propel him into a dominant position as this epic campaign enters its final month.

A Wall Street Journal poll found that he has widened his lead over Mr McCain to six points, mainly because he was far more trusted to handle the financial crisis.

About one in three voters said they were "more reassured" by Mr Obama's approach, compared to just 25 per cent who said the same about Mr McCain.

A Washington Post/ABC News survey in the critical battleground of Ohio gave Mr Obama a six point advantage among likely voters. No Republican has ever won the White House without the Buckeye State and again, it was the faltering economy boosting Mr Obama's fortunes.

Frustration at falling behind Mr Obama in opinion polls has begun to boil into anger at Republican rallies with Mr McCain and Sarah Palin.

Events this week have been marked by ugly outbursts from crowds. In Clearwater, Florida, shouts of “kill him!” could be heard amid a chorus of boos when Mrs Palin attacked the Democratic nominee over his links with 1960s radical, Bill Ayers.

Journalists were reported to have been taunted with obscenities or racial insults from members of audience when Mrs Palin blamed the “mainstream media” for what she described as her “less-than-successful” - and much-parodied - television interviews.

At a rally on Monday in Albuquerque, New Mexico, Mr McCain asked: “Who is the real Barack Obama?” A man in crowd screamed back the reply: “Terrorist!”

The Republican nominee and his running mate cannot be blamed for such incidents. But their campaign is increasingly playing to the fears some voters harbour about the multi-ethnic background of Mr Obama - or paint him as a typical “Chicago politician” with ties to corrupt and dangerous individuals.

In Jacksonville today, Mrs Palin continued her assault on Mr Obama's character. "This election is about the truthfulness and judgment needed in our next president. John McCain has it, Barack Obama doesn’t," she declared.

Speaking ahead of the TV debate between the two candidates, she added: "We’ll see the difference...between a politician who observes and analyses us, and a leader who knows and understands us."

The Democratic campaign has sought to counter-punch by exhuming old controversies about Mr McCain, including his role in the "Keating Five" scandal in 1989 when he was one of five Senators criticised for intervening on behalf of the head of a failed investment company from whom they had received political donations.

Yesterday, Mr Obama's aides pointed out the past connections Mr McCain had with a private group that supplied aid to guerrillas seeking to overthrow the left-wing government of Nicaragua in the Iran-Contra affair during the 1980s.

But he has also sought to claim that Republican attacks are merely an effort to distract voters' attention from the economy. A new advert aired by his campaign yesterday, says: "As Americans lose their jobs, homes and savings, it's time for a president who'll change the economy, not change the subject."

A spokesman said: "In order to change the dynamics of this race, we anticipate that McCain will launch his nastiest attacks and continue to lie about Barack Obama’s record and his vision to fundamentally change our country. We fully expect that his “turn the page” strategy to ignore the economy will be seen in full view for 90 minutes of character attacks against Barack Obama."

Despite his troubles, the format for tonight's debate at Belmont University in Nashville - in which the two candidates will sit in director's chairs and answer questions from voters, including some posed over the internet - should suit Mr McCain who favours town hall settings.

He has repeatedly challenged Mr Obama to a series of ten such encounters across the country. The Democrat has refused, saying that the three formal presidential debates are sufficient.

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