With control of the House of Representatives and the Senate hanging in the balance, rival candidates are plumbing new depths of taste and duplicity in their desperate quest for votes.

“Brad Miller spent your money to study the masturbation habits of old men,” says an advert paid for by Vernon Robinson, Mr Miller’s Republican opponent for a North Carolina district. These advertisements also allege that Mr Miller failed to support the purchase of better body armour for soldiers in Iraq, saying that he “votes for sex but not for our troops”.

Mr Miller was in Iraq at the time of that body armour vote, while his interest in elderly men masturbating appears limited to his opposition to a Bill scrapping federal grants for sexual studies.

In Tennessee this week the Republicans broadcast an advert showing an attractive, bare-shouldered blonde saying that she had met Harold Ford Jr, the Democrat senatorial candidate, at a Playboy party. It concludes with her winking into the camera and whispering: “Harold, call me.”

Mr Ford, who is trying to become the first black senator for the South since the American Civil War, was one of 3,000 guests at a Playboy party for the Super Bowl last year. Black groups have complained that the advert, which has now been withdrawn by the Republicans, was playing up to the residual sensitivity of southern voters towards inter-racial dating and possibly a stereotype of African- American males.

In Pennsylvania, Democrats have run an advert showing mocked-up newspaper headlines about an affair by Don Sherwood, a Republican Congressman, in which he was accused of “repeatedly choking” or “attempting to strangle” his mistress. Mr Sherwood was forced to run his own advert admitting his affair but denying that he tried to kill anyone.

In Missouri, actor Michael J. Fox, who is afflicted by Parkinson’s disease, has waded into the Senate race on behalf of Claire McCaskill, a Democrat challenger. In a TV advert, where his head lolls from side to side, he claims that Jim Talent, the Republican incumbent, would criminalise the stem-cell research that may help Parkinson’s sufferers. The right-wing radio talk-show host Rush Limbaugh was forced into a grudging apology after accused him of either acting or failing to take his medication. Doctors have since cleared Fox of exaggerating his condition, but not before Republican stem-cell research opponents broadcast their own advert featuring celebrities who claimed that the Democrats were raising false hopes and trying to make cloning legal.

American analysts are fond of pointing out with pride that attack adverts have been part of the heritage of presidential elections at least since the days of Abraham Lincoln. But midterm campaigns have tended to be slightly more dignified — until now. “I think 2006 will prove to be the most negative campaign in memory,” said John Geer, a political scientist at Vanderbilt University, and the author of In Defence of Negativity. “Control of Congress is in question. That competition creates the perfect environment for a really negative race.”

According to the Centre for Responsive Politics, the elections will cost $2.6 billion (£1.4 billion) this year — an 18 per cent increase over 2002, when midterm elections were last fought. The combined spending of all parties in last year’s British general election campaign — in which TV advertising was outlawed — was substantially less than £50 million.

Much of the American spending will happen between now and polling day on November 7, with the Republicans promising to use their cash advantage to pay for a blizzard of negative TV advertising.

Pennsylvania’s Republican Senator Rick Santorum is screening an advert depicting Bob Casey, his Democratic challenger, alongside Kim Jong Il, the North Korean leader — and a mushroom cloud — to highlight his rival’s opposition to missile defence.

The Democrats merely need to broadcast images of the President to be negative. But the Republican strategy this year has been to shift the focus away from George Bush and the Iraq war towards the character and record of the individuals standing against them. For instance, Steve Kagan, a Democrat doctor running for Congress in Wisconsin, is being attacked for having once sued patients who did not pay their bills.

Some candidates are even running their own adverts denouncing their opponents’ attacks. These include Chris Murphy, a Democrat, who has been portrayed by an actor in Republican adverts receiving a warm welcome when he visits the home of a drug dealer. His response is to broadcast adverts accusing Nancy Johnson, a Republican, as being willing “to do anything to stay in Congress”.

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