NEGATIVE political campaigning is an abomination.

All politicians agree about that. They agree until, sadly, it becomes necessary to sanction a few ads built on half-truths, character assassination, and naked fear. They take the step with a heavy heart, obviously, and only to counter the filthy misrepresentations put about by their opponents.

Negative campaigning works: that's the dirty, not-so-secret, self-evident truth. Voters like to believe they are unimpressed by propaganda. They tell themselves they can see through a politician who would rather rubbish his rivals than boast about his own record. But drop a tax bombshell, mention a fiscal black hole, suggest that the other guy is dishonest or, worse, "soft"(on anything), and watch what happens.

The phenomenon is both universal and depressing. In the end, it doesn't do anyone any good. But if negative campaigning is pernicious in what we still call a democracy, how much worse is negative voting? That's when you exercise your precious franchise not to achieve a desired result, but simply to forestall the alternative. It happens when you can see few enough good reasons to vote for someone, but plenty of reasons to ensure that the other character gets nowhere near power. It is a sterile business, but rational. It also exposes the limits of what passes for choice.

We've had experience enough of the phenomenon in Britain – it's one reason why we have an inept Coalition Government – but in America this ideological gridlock is being brought close to a weird kind of perfection. A presidential campaign is being fought out between an incumbent whose once-avid supporters are deeply disillusioned and a challenger distrusted by his own side who got the job by default.

Barack Obama and Mitt Romney are, by common consent, neck and neck. Not for the first time, American voters are split almost precisely down the middle. But this is not because Republicans have found a champion who articulates an inspirational alternative. It is not because Democrats have been galvanised by a profound belief in hope and change. Everything turns on averting the horror of a win for the other lot. As beacons of hope go, the election is a sputtering candle.

Mr Obama addressed his party's convention in Charlotte, North Carolina, on Thursday with an apology disguised as a speech. Instead of celebrating all that has been achieved since he promised to rescue America from economic misery, he pleaded for more time, begged for patience, and in effect – for no other explanation fits – confessed his failures. Above all, he issued dire warnings of the fate awaiting ordinary Americans if the Mormon plutocrat and his conservative backers win in November.

Mr Obama wasn't wrong. If you believe what you hear, a Romney administration is liable to be reckless in foreign policy, toxic for the global economy, indifferent to the fate of the planet, and wholly self-serving. You needn't be American to worry about the prospect of President Romney. The fact remains that the prospect is only plausible, first, because Mr Obama has failed; second, because a huge chunk of the American electorate would detest him even if he was producing miracles on a daily basis.

In the US, the habit of negative voting has become ingrained. In his first presidential campaign Mr Obama attempted to banish the spectre: that was the point, in part, of all those speeches about change. He offered voters the belief that things could be different. But Republicans, most of them, never bought it. The rest, Democrats and independents, have shed their illusions since. Now only fear remains.

A lot of people will vote for Mr Romney because of what is, in essence, a giant negative advertising campaign. Too few will remember that America's economic woes began under George Bush and the Republicans. A deficit of $1.6 trillion and a national debt exceeding $16 trillion were not Mr Obama's creations. Though official unemployment in the US fell slightly yesterday to 8.1%, and though the rate remains stubbornly high, it is a problem the President inherited. He is culpable, if culpable, only for failing to get Americans back to work.

But then, that is exactly what he promised to do, just as he promised to reform Wall Street, shut Guantanamo, guarantee health care for every citizen, and restore America's infrastructure. The best Mr Obama can claim – and he is reduced to this very claim – is that things are not worse than when he started, or as bad as they might become should Mr Romney get the nation's top job.

As far as it goes, this is fair enough. But how far does it go? He told the convention he would restore fairness in American life. Democrats, nominally on the left of the American spectrum, like that sort of talk. But many will ask – have asked – why they are still waiting. They will further ask why they should believe Mr Obama this time, especially after his punishment of Wall Street amounted to nothing more than tough talk accompanied by a ton of free money for unreformed banks.

Having asked their questions, Democrats and independents will pause. Mr Obama is counting on it. Such voters will pause and ask a last, very simple question: what's on offer instead? Mr Romney, who cares nothing for the rights of women, for the middle (they mean working) class, who still believes that the rich have had too few tax cuts, who understands politics as nothing better than a business proposition?

On both sides, the American electorate is being herded by fear. This is not, needless to say, a healthy state of affairs. It is barely worth the name – not that we should talk – democracy. It also carries a profound risk for Mr Obama. If voters are fixed on the state of the economy they might simply conclude that, one politician having failed, his rival might as well have a chance. Whether Mr Romney "understands" the working class or possesses a single consistent belief could be of lesser importance.

"I won't pretend the path I'm offering is quick or easy," Mr Obama told Democrats and the country. "You didn't elect me to tell you what you wanted to hear. You elected me to tell you the truth. And the truth is it will take more than a few years for us to solve challenges that have built up over decades."

The President was honest, by his lights, but wrong. In his last campaign he quite deliberately led those voters to believe that it would not take "more than a few years" to solve their problems. And those people, with real wages falling, certainly did elect him "to tell you what you wanted to hear". They also wanted it to be true. It wasn't; it isn't.

Mr Romney will have the support, meanwhile, of a mass of certifiable types who believe they are fighting the advent of a black socialist overlord whose tyranny, thus far, has extended to some half-hearted healthcare reforms. Yet such people neither like nor greatly trust their own candidate. Mr Romney is, for conservative patriots, merely the less appalling alternative, the mirror image of what Mr Obama has become for so many of the people he inspired only four years ago.

Americans could ask themselves, as we could ask ourselves, how and why the political process became a business of affirming negatives, of voting out of fear rather than hope. The answers might be interesting, but they would not be comforting. These things are no accident, after all.