President Musharraf's resignation yesterday, forced on him by the threat of imminent impeachment, leaves Pakistan leaderless at a critical moment.

In the tribal areas separatists, Islamist extremists and Taleban supporters are in open revolt against the central government. Kashmiri militants are preparing new cross-border attacks against India. Arms are pouring into Afghanistan to fight Nato troops, while al-Qaeda leaders plot terrorism from their border hideouts. The shadowy Inter-Service Intelligence (ISI) agency, intent on a proxy war with India, is moving away from government control. The economy is stalling, with inflation running at 25 per cent and trade and fiscal deficits widening. And in Islamabad politicians bicker over whether to prosecute Mr Musharraf or allow him to retire with dignity.

Rarely has a power vacuum been so dangerous. Pakistan has 160 million people and a nuclear arsenal. It also has all the makings of a failed state: a fissiparous polity, an unequal and quasi-feudal society, tribal and regional rivalries, religious animosities and extremism, weak central government and a corrupt political class. In his televised defence of his record, Mr Musharraf said he had assumed power when Pakistan was about to be declared a terrorist state and an economically failed state. He underlined the tragic cycle of poor leadership and lost opportunities.

And yet a solid, largely urban, middle class exists that has prevented extremism getting a grip. It rejected Islamist parties at the last election. It stood firm against the imposition of emergency rule and Mr Musharraf's final unwise attempt to muzzle the judiciary. This middle class has, so far, provided the backbone that has held the country together and shown firm attachment to moderation and democratic values. It was to this class that Mr Musharraf appealed after his coup, and his initial actions in its support remain his legacy: the fight against corruption and venal politicians, the empowerment of women at local level and his consistent stance in favour of peace with India and against Islamist terrorism.

How should Mr Musharraf be replaced? Asif Zardari and Nawaz Sharif, the leaders of the Pakistan People's Party and the Muslim League, insist that the presidency should be purely a ceremonial office - although Mr Zardari has made no secret of his ambition to hold the job and with it some of Mr Musharraf's powers. The fragile coalition could soon founder as the two men argue over the presidency and its potency.

The constitution has been altered so often that most people are no longer sure what it stipulates. But several things ought to be clear. First, if Pakistan is to avoid a prolonged political deadlock, a credible figure needs to be found soon.

Secondly, the President's powers need to go far beyond the nominal. Pakistan's hybrid parliamentary-presidential system has been a recipe for political deadlock, and to prolong such uncertainties at a time when the country needs leadership and continuity would be to play into the hands of a venal and irresponsible political class.

Thirdly, the Army's position must be clear - not only because of its record of frequent intervention, but because of its key role in the main challenges: the war in Afghanistan, the fighting in the tribal areas, the curb on cross-border terrorism in Kashmir and detente with India. On all four issues, things are unravelling dangerously.

Few countries face as many challenges or are as critical to regional and global security as Pakistan. The country needs clear and decisive leadership. If the politicians cannot agree on a figure who can rise above the squabbles in Islamabad and endow him with the powers needed be effective in office, they should call for a popular vote. Democracy is always the best answer.