When President George W. Bush and Senator John Kerry face off tonight in their first election debate, the rest of the world will see a reflection of unrivalled military might and financial muscle that nonetheless is losing influence, friends and global respect. This tension between power and legitimacy emerged as a dominant theme among world leaders meeting at the United Nations last week. It is likely to set the parameters for the one-hour debate in Florida on US foreign policy and security.

Neither candidate is likely to dispute America's unchallenged power in what they both see as a "unipolar" world. But the Iraq war has exposed the limitations of force backed by ad hoc coalitions of convenience. How the US should wield authority lies at the heart of their foreign policy differences.