Leading article: A make or break election in Afghanistan

Thursday's vote will also determine how the Nato intervention proceeds

It is hard to avoid the impression that the contest for the future of Afghanistan is coming to a head, and with it the role of British forces there. This weekend saw the total of British deaths pass 200, a toll that has accelerated in recent months as the military has engaged with the Taliban in Helmand province. Although Panther's Claw, the operation intended to prise a small but sensitive area of the south from the Taliban's grip, is officially over, the casualty rate – mostly from roadside bombs – continues to be heavy.

Each new flag-draped coffin unloaded at RAF Brize Norton inevitably raises further questions about the costs and benefits of British involvement. Public opinion has tolerated the losses so far, as befits a country with a proud military tradition, but polls suggest support is waning. The material costs could also rise if concerns about the provision of equipment are to be met. This is an expensive intervention in every respect.

The rising cost, not just for Britain, but for the United States too, is one reason why the elections to be held this Thursday are so crucial. Only the second presidential election to be held since since the US-led intervention that followed the terrorist attacks of 9/11, they are just as crucial as the first, if not more so.

The sad truth is that Afghanistan seems as far from peaceful rebuilding as ever. Rather than waning, as might have been hoped after so many years of effort, the violence has been mounting. The authority of the President, Hamid Karzai, appears to be seeping away; regional warlords and the Taliban have retrenched, capitalising on the West's failure to improve people's lives.

As until recently in Iraq, we watch a vicious circle of Western reconstruction efforts thwarted by lack of security – a failure which then gives rise to further insecurity, further deterioration of the infrastructure and growing resentment at the foreign military presence. President Obama and his new diplomatic and military team have set about trying to change this, by using military power more judiciously and concentrating efforts on co-operation with the local population. Attempts are also being made to co-opt less extreme elements of the Taliban.

Success, though, is far from guaranteed. How these elections proceed will be a gauge not just of the popularity of the Karzai government, but of the progress, or lack of it, towards a stable Afghanistan. How many people, especially women, feel safe enough to go to vote at all will be one key indicator; another is how many voting booths are open. With the Taliban threatening to target polling stations, the attack on Nato's headquarters in Kabul suggests that even the heaviest protection may not be enough. And if – because of low turnout or an insufficient majority – there is no victor in the first round, the need for a second round could exacerbate the present uncertainty into October and beyond.

A respectable turnout with a clear result would be the most satisfactory outcome. The US, which appears in two minds whether to continue backing Mr Karzai, would then be able to tailor its policy to something akin to a democratic mandate. A credible election would also help Gordon Brown: it would show recent casualties as just one side of the balance sheet, and perhaps convince the public to keep faith with the mission a little longer. That said, the Defence Secretary said yesterday that Britain would increasingly concentrate on training Afghan forces – a hint, perhaps, that a contingency is being prepared that can be presented as evidence of progress, even as it heralds the start of a retreat.