The attack ad was unveiled last week and yet the furore over the Obama campaign's suggestion that Mitt Romney, the Republican candidate for the American presidency, had contributed to a woman's death from cancer is still causing waves.

The battle for the presidency has got dirty, less than three months before the election on November 7.

The mud was flying yesterday over comments by Vice-President Joe Biden, interpreted as racist by Romney, who is hammering the President for a campaign about "division and attack and hatred".

But the contest is at its dirtiest in the attack ads deployed by both Democrats and Republicans to an unprecedented extent in this campaign.


The candidates themselves can - just about - remain above the fray while their so-called Super-PACs, allowed to spend limitless funds on the campaign thanks to a Supreme Court ruling, are pouring millions into destroying the other side.

One of the most controversial negative ads so far features a Missouri steelworker, Joe Soptic, who lost his job at a factory owned by Bain, the private equity firm once run by Romney.

As a result of his layoff, his family lost their health insurance - a factor which, according to the ad by the pro-Obama Priorities USA Action, contributed to the subsequent death of Soptic's wife, Ilyona, from cancer.

Despite widespread protests about the ad picked up by US media, and with some Democrats saying it was too harsh and in fact inaccurate, the Obama campaign has continued to promote it online and on Wednesday it ran in the swing state of Ohio because of a TV "station error", the Super-PAC said.

Since Romney nominated Congressman Paul Ryan as his presidential running-mate he has been accused by the Democrats of "pushing granny over the cliff" by picking the House budget chairman best known for his plans to radically overhaul Medicare benefits to the elderly. The Obama campaign lost no time in producing an ad in which retirees in Florida expressed concern about a future Romney Administration "ending Medicare as we know it".

But on Wednesday, the Romney campaign hit back with an ad claiming that Obama has diverted US$716 billion ($888 billion) from Medicare funding into his signature health reforms adopted last year.

At a campaign stop in Ohio, the former Massachusetts Governor repeated the charge against Obama: "He is taking your money to finance his risky and unproven takeover of the healthcare system," Romney told a rally in Chillicothe. "We will not let Obamacare happen."

The prime target of the attack ads is the swing voter, the independents who are not affiliated to either political party and whose ballots will be crucial.

But are the negative ads effective?

Dr John Geer, professor of political science at Vanderbilt University, who has teamed up with the YouGov research firm on a systematic study of independent voters' views on the attack ads, told the Herald that he was "quite sceptical about the power of these ads" despite their record number. "They are pretty ephemeral, and they die out pretty quickly," he said.

His study of about a dozen ads so far with a sample of 600 Americans showed that as a general rule, the Obama campaign attacks on Romney have more impact, but those surveyed said they would not vote for Obama as a result. "They don't move the polling numbers," said Geer. "After all, they've seen him in action for the past three years."

So why have the Super-PACs spent a reported US$343 million since April on the negative ads? According to Geer, they are also targeting the media, which can amplify the message. That's what happened with the Swift Boat ads that doomed Senator John Kerry's presidential hopes in 2004 by smearing his military record in Vietnam. And that is campaign gold.