The decision to cancel a second round in Afghanistan’s presidential election is welcome and right. After the withdrawal of Abdullah Abdullah, the former Foreign Minister and principal challenger to President Karzai, it would have been farcical to hold a run-off election with only one candidate. The Taleban would have used the delay to intimidate the population and the election as a chance to harass and kill Nato soldiers attempting to protect the ballot. Would Britain, or any Western power, have gained anything in advancing democracy by sacrificing its troops to guard booths offering only one choice?

Dr Abdullah’s decision is as shrewd as it is inconvenient. He knew that he had little hope, as a Tajik, of winning votes among the Pashtun majority and virtually no chance of beating Mr Karzai, however closely scrutinised were the returns from those areas where the blatant cheating and fictional results so discredited the first round. After strong private pressure from the West, he stopped short of calling for a boycott of the election. This would have again jeopardised the legitimacy of any declaration of a winner and given the Taleban further cover to campaign against the “corrupt” Government in Kabul.

He now has considerable moral and political leverage, however, to demand a say in the new Government to be headed by Mr Karzai. The incumbent President may be as unwilling to concede any power sharing as he has been to clean up his corrupt, unstable and discredited earlier administration. The US and its Western allies should leave him in little doubt that he has no alternative. Without a government that represents a semblance of national unity, the factionalism and tribal rivalries that have so undermined Kabul’s authority will continue. Nato countries have found themselves in the invidious position of propping up a government of dwindling legitimacy within Afghanistan and growing unpopularity among its voters at home.

For its pragmatic endorsement of Mr Karzai’s dubious re-election, there must be a price. Western governments have a right to demand changes in those ministries, particularly of the interior and defence, where corruption has been most blatant. They are supporting Afghanistan’s reconstruction to the tune of about $10 billion and with the lives of their soldiers. A weakened Karzai is in no position now to continue his insouciant refusal to heed their warnings or reform and improve up his administration.

An end to this sorry and drawn-out exercise in Western democracy does now make it easier for the West to take the long-term strategic decisions that have been postponed too long. The most pressing is the reinforcement of the US forces. President Obama has refused to be rushed, insisting on broad consultation with his military and diplomatic advisers. That consultation has gone on long enough. There will never be consensus on an issue so vexed, so domestically divisive and internationally perilous. Mr Obama must now decide whether to send the 40,000 troops requested or some lower figure. His Nato allies must also decide on their matching response. More troops will not alone win the war or crush the Taleban. They will, however, be a signal of the resolve without which Nato’s deployment is wholly irrelevant. And that political resolve must begin with Mr Karzai himself.