Dr Dana Allin, senior fellow for Transatlantic Affairs at the International Institute for Strategic Studies in London, commented: "Unquestionably there is going to be a change in American presentation to the world on a number of key issues.
"In all three cases (McCain, Clinton and Obama) there will be a much more unequivocal renunciation of torture.
"On broader international issues (such as climate change), there is a commitment from all three to take a different US approach. "
07 February 2008: BBC News
By Paul Reynolds
World affairs correspondent BBC News website
The world is sitting up to take notice of an intriguing US presidential election campaign as the Bush era of US foreign policy draws to an end.
The importance of who is in the White House is illustrated best by President George W Bush himself. If Al Gore had won the election in 2000, it is unlikely that the US would have invaded Iraq.
In a speech in September 2002, Mr Gore predicted one of the consequences that might flow from an invasion, one which many in the US and around the world are now looking to this election to resolve. It had, he said, "the potential to seriously damage our ability to win the war against terrorism and to weaken our ability to lead the world in this new century".
There is a sense now that the rest of the world has an opportunity to re-engage with the United States.
"They feel there's a real chance to work with the US," said Julianne Smith, a senior fellow at the Center for Strategic and International Studies in Washington. "America's image in the world is really on the line."
Non-Americans, she said, were looking for someone who could "restore faith in the United States."
'Unquestionably, a change'
Dr Dana Allin, senior fellow for Transatlantic Affairs at the International Institute for Strategic Studies in London, commented: "Unquestionably there is going to be a change in American presentation to the world on a number of key issues.
"In all three cases (McCain, Clinton and Obama) there will be a much more unequivocal renunciation of torture.
"On broader international issues (such as climate change), there is a commitment from all three to take a different US approach.
"There will be less of a dramatic change in strategic foreign policy, largely because change has already come.
""The salience of an aggressive or assertive policy of pre-emptive war has been lowered anyway because of Iraq.
"But Barack Obama for one wants to end not only the war in Iraq but what he calls the mindset that led to the war."
The Iraq factor
Iraq highlights the major differences between the front-runners. Senator Obama is talking about the US pulling out by the end of 2009. Senator Clinton speaks of starting to withdraw within the first 60 days of her administration but has no end date.
However, Senator McCain, whose career as a naval officer and a politician has been based on the security of the United States, has said he does not mind if US troops are in Iraq "for a hundred years".
He was in favour of the US reinforcement into Iraq last year and his prediction that it would have an effect has stood him in good stead during the election campaign.
Talking to a town meeting in Derry, New Hampshire on 3 January, he remarked that US troops had been in Japan and South Korea for about 60 years and it would be "fine" with him if they stayed in Iraq "so long as Americans are not being injured or harmed or wounded or killed."
A McCain presidency could be something quite volatile, given his commitments on US security.
