Whoever wins the election in November, it is already clear that the next US president will make a significant break with George W. Bush's approach to the "global war on terror".

Excluding Mike Huckabee, who has admitted it would take a "miracle" for him to take the Republican nomination, the remaining presidential contenders - John McCain, Barack Obama and Hillary Clinton - have all pledged to repudiate key elements of Mr Bush's counter-terrorism policies.

All have pledged to close Guantanamo Bay, the Cuban detention centre that has attained notoriety round the world. All have unequivocally pledged to put an end to torture, including "waterboarding", which the Bush administration last week again declined to define as "torture" and refused to rule out in future.

Mr McCain, who suffered torture when he was a prisoner of war in Vietnam, has been the only candidate among the leading Republicans to oppose the practice, which he has insisted never produces good intelligence and also compromises America's moral authority.

Mitt Romney and Rudy Giuliani both supported "enhanced interrogation techniques", which is widely taken as a euphemism for torture. In one presidential debate, Mr Romney said that far from closing Guantanamo Bay, he believed it ought to be doubled.

"We can safely say that whoever among them becomes the next president would never entertain the idea of torture as a useful instrument of US policy," says Larry Wilkerson, a former military officer and chief of staff to Colin Powell, who was Mr Bush's first secretary of state. "Even in the Bush administration, people like Bob Gates [the secretary of defence] and Condoleezza Rice [the secretary of state] argue every day against torture and for the closure of Guantánamo, only to be vetoed by Dick Cheney."

Against expectations, the next president, Republican or Democrat, will also take an aggressive approach to tackling global warming - again, in marked contrast to Mr Bush's record.

Alone among the leading Republican contenders, Mr McCain has proposed a "cap and trade" system for carbon emissions that is similar to the plans put forward by Mr Obama and Mrs Clinton.

All three contenders propose negotiating a successor treaty to the Kyoto protocol, which was never ratified by the US Senate and which Mr Bush disowned on taking office.

All three also signify a clear break with Mr Bush's history of partisanship by touting their abilities to "cross the aisle" and work with the other party.

Kurt Campbell, head of Centre for a New American Security, a centrist think-tank in Washington, says: "This has been a tough election so far and will be a tough general election but the points of commonality are really striking.

"They all preach bipartisanship and they all - including Mr McCain, who is very clear about this in private - believe Mr Bush has gone badly astray in his foreign policy management."

However, Mr McCain's strong support for Mr Bush's Iraq troop "surge" and his bellicose stance on Iran provides a sharp difference with both Democratic candidates and suggests that disputes over the Middle East will play a central role in a general election.

There are also sharp differences on the economy, with Mr McCain proposing to make Mr Bush's tax cuts permanent but both Democrats supporting a repeal.

In addition, Mr McCain is under pressure to water down what many conservatives believe are his "liberal" positions on the "war on terror" and global warming in order to unify the Republican party for the general election.

By Edward Luce, The Financial Times, February 12 2008