Barack Obama declared today that Republicans will try to demonise his wife Michelle to undermine his presidential bid, as his campaign unveiled a new website to debunk false rumours about the couple's faith and patriotism.

In a speech at a fundraising event in Chicago, Mr Obama said: “They're going to try and make me into a scary guy. They're even trying to make Michelle into a scary person.”

His comments come after an intensifying effort by some Republicans to target Mrs Obama, an attack campaign very similar to tactics used against Hillary Clinton when her husband ran for the White House in 1992.

Just one week into the general election battle, and despite pledges by Mr Obama and his Republican opponent John McCain to run a “different” campaign without smears, attacks and based solely on the issues, it is already showing signs of degenerating into depressingly familiar terrain.

In the past week, both men have deliberately distorted each other's policy positions. Mr McCain, the victim of a scurrilous smear campaign during his 2000 nominating battle against President Bush, said on Wednesday that he can't control every attack advertisement against Mr Obama, and expected himself to be a target. Surrogates in both camps have sent a barrage of e-mails into reporters' inboxes trying to make each candidate appear dangerously extreme.

The head of Mr Obama's vice-presidential vetting team was forced to resign amid accusations of receiving favourable mortgage rates from a company at the centre of the sub-prime lending crisis. The Democrat's campaign is now levelling the similar charges against a member of Mr Mccain's running mate search group.

On the new Obama website - fightthesmears.com - the first entry deals with a rumour that a video exists of Mrs Obama in the pulpit of the church made infamous by her husband's former pastor using the racially-charged epithet “whitey”.

The website states: “No such tape exists. Michelle Obama has not spoken from the pulpit of Trinity [United Church of Christ] and has not used that word.”

The campaign, in an unprecedented pre-emptive strategy, has asked millions of online supporters to track down internet rumours suggesting Mr Obama is a Muslim, or that he and his wife are dangerous radicals, so that they can be posted and knocked down by Mr Obama's aides.

The prime focus against Mrs Obama, who has been given her own team of handlers and advisers, is a comment she made in February that “for the first time in my adult lifetime, I am really proud of my country.”

She later clarified the statement, saying her pride was in the political process. On Monday she was even defended on the issue by Laura Bush, the First Lady.

This week, Lawrence Eagleburger, a former Republican Secretary of State, introduced Mr McCain's wife Cindy as somebody who was “proud of her country, not once but always.” “This is politics American style 2008. The wives are fair game,” said Jonathan Capehart, a political analyst.

Last month, Mr McCain proposed a series of 10, unmoderated, free flowing “town hall” debates to discuss the issues, an idea Mr Obama said he found “appealing”. Now their advisers are locked in negotiations, with the prospect of such open forums, and such a number, rapidly diminishing.

“Regardless of what they want to do, at the core all these forces that are usually involved in a political campaign - demonise your opponent and embellish your talents - are very powerful,” said Stephen Hess, at the Brookings Institution think tank.

“We're not going to turn around human nature.”

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