President Asif Ali Zardari, Benazir Bhutto's widower, formerly known as Mr Ten Per Cent because of kickbacks received during his wife's time in office, has become one of the most powerful and potentially dangerous men in the subcontinent. Mad and bad. And now omnipotent. He is head of state, supreme commander of the armed forces, has the power to dismiss parliament, appoint the heads of the army and election commission – and, as chairman of the National Command Authority, has the final say in the deployment of nuclear weapons.

Earlier Zardari vowed to relinquish the executive powers that Pervez Musharraf gave to the originally ceremonial presidency. Now he's evasive. Despite the fact that he has little public support (14 per cent, according to a recent poll), holds no seat in parliament and has no mandate other than his association with the Bhutto name, he had every right to nominate himself or anyone else as President. His party – inherited from his late wife – was democratically elected in February and has the largest number of seats in parliament.

The man who now has his finger on the nuclear button was only last year declared unfit to stand trial in a UK court on account of multiple mental problems. According to court documents filed by his psychiatrists, he suffers from dementia, major depressive disorder and post-traumatic stress after spending 11 of the past 20 years in jail in Pakistan. According to their testimony last year, he found it hard even to recall the names of his wife and children.

He has long had memory problems. In the past he has been unable to recall whether he was the owner of a multimillion-pound Surrey estate (he thought not, but later took possession of it) or if $60m (£34m) in a frozen Swiss bank account was actually his. He also thought that he had graduated from the London School of Economics, or was it the London School of Business Studies? There are no records of his doing either.

The doctors' diagnoses of severe mental ill-health rid Zardari of his corruption case in the UK. Last November's National Reconciliation Ordinance, brokered by the Americans to allow Bhutto's return to Pakistan and passed by Musharraf, rid him of the rest. It also guaranteed him lifelong immunity from prosecution for corruption. He appears to have made medical history and rid himself of his dementia in time to become President. The only thing he can't shake off is his appalling reputation.

Zardari has long been dogged by allegations of crime and corruption. In 2003, a Swiss magistrate found him guilty in absentia of laundering $10m. Musharraf's National Accountability Bureau estimated that he had looted up to $1.5bn from the treasury during his wife's two terms in office. In 1990, he was in trouble for allegedly tying a remote-controlled bomb to the leg of a businessman and sending him into a bank to withdraw money from his account as a pay-off. More sinisterly, he was charged with complicity in the murder of his brother-in-law Murtaza Bhutto, but the case was never tried. He was also implicated in the 1996 murder of a judge, Justice Nizam Ahmed, and his lawyer son.

Even if Zardari is given the benefit of the doubt and has changed after his wife's assassination and his many years in jail, his behaviour in the run-up to his election as President proves he still can't be trusted. He has already reneged on several written agreements made with the coalition, including his pledge to field a non-partisan candidate for president, as well as his pre-election promise to reinstate the judges deposed by Musharraf. If reinstated, they could repeal the amnesty granted to him and reopen corruption investigations.

Inside Pakistan, people are despondent. The economic situation is worse than ever, with inflation at almost 25 per cent. Outside Pakistan, despite his reputation, he is tolerated. He's seen as pro-West. He will be another "key ally in the war on terror".

America is stepping up its military campaign in the region, not least because George Bush wants Osama bin Laden's grizzled head before the US presidential election on 4 November. Strikes against Pakistan's tribal areas by US/Nato forces are not uncommon, but on Wednesday, for the first time, ground forces attacked a village on the Pakistani side of the border, in South Waziristan, killing 20 innocent people. Tribesmen are up in arms – literally – and have promised revenge, and there has been widespread condemnation. If Zardari is seen to be tolerating such attacks by foreign troops inside Pakistan, a violent backlash is likely.

On Friday, he pledged to eliminate the Taliban. A tall order. Since Musharraf joined the "war on terror" at US bidding and expense and sent Pakistani troops into the Federally Administered Tribal Areas, Pashtun tribesmen have been falling over their Kalashnikovs to join the Taliban. With hundreds of thousands of internally displaced people from Bajaur as a result of conflict, weekly reports of aerial attacks and collateral damage, the Taliban movement is growing in strength by the day.

And it's not just the formidable Pashtuns on the warpath. The Taliban is operating on fertile soil. Nationwide, 71 per cent of Pakistanis oppose co-operating with the US in counterterrorism and 51 per cent oppose fighting the Taliban at all, according to a June Gallup poll. The vast majority of Pakistan's 190 million people may not like the Taliban, but they dislike the US and what is seen as its proxy army even more. Even within the army, there are rebels who object to being forced to kill their own people. The majority of the population is also deeply opposed to what it sees as a foreign occupation in Afghanistan, with more than 80 per cent favouring a negotiated settlement and withdrawal.

Suicide attacks within Pakistan – unheard of before 9/11 – are now so commonplace they barely make the front pages. From the wilds of the tribal areas to the mosques of west London, the war on terror has been hopelessly counterproductive, despite being fuelled by millions of dollars. Its chief beneficiaries have been the Taliban and their sympathisers who feed on the instability.

Zardari has replaced Musharraf, but their policies will be the same. He is unlikely to prove more successful at tackling extremism. His already meagre popularity rating is expected to dwindle rapidly as he is increasingly perceived as another US stooge. And despite all his powers, he is still less powerful than the army. As ever, if the politicians fail to steer Pakistan through its myriad problems, the military, which has notched up 33 years of rule in Pakistan's 61-year history, will step in.

What is depressing is not that everything now changes with the election of Asif Ali Zardari, but that everything stays the same.