The literature on American exceptionalism reveals two dominant themes that influence foreign policy. First is that of the US as exemplar: by her example, America can demonstrate to the world the distinct benefits of an adherence to liberty, equality, and justice. The second is that of the US as a missionary nation, adopting a more assertive posture to projecting those ideals both, at home and abroad.

The two strands of thought can be contextualised as producing different approaches or roles in the conduct of US foreign policy. The exemplar belief results in the US adopting a stewardship role in the world. The missionary belief results in an American leadership role.

The stewardship/leadership divide transcends party lines. Consider the driving leadership of Democrat Harry Truman in mobilising an exhausted and savaged world in the aftermath of the Second World War. Or the disciplined and deft stewardship of George HW Bush in dismantling the vestiges of the Cold War and crumbling Soviet Union.

The immediate instinct is to assign a value judgment and view stewardship as representing an inferior quality to leadership, but this is not the case. The two roles are well suited to different times and poorly suited to others. They can also be implemented with different levels of competence and with varying degrees of success. Presidents Carter and Reagan both subscribed to the American leadership role, and in not too dissimilar times, but with dramatically different outcomes.

The central plank of the Romney foreign policy platform could not be clearer. The US is an exceptional nation and it is not only duty-bound to lead, but leading is in America's best interests.

Senator John McCain told the GOP delegates that 'the demand for our leadership in the world has never been greater. People don't want less of America, they want more.' Condoleezza Rice continued: 'We do not have a choice. We cannot be reluctant to lead – and we cannot lead from behind.' Vice-presidential candidate Paul Ryan promised, 'We will act in the conviction that the United States is still the greatest force for peace and liberty that this world has ever known.'

Romney closed by committing to a return to the bipartisan foreign policy of Truman and Reagan. 'We will honour America's democratic ideals because a free world is a more peaceful world.'

President Obama's foreign policy demonstrates a distinct bias toward the stewardship role and reveals the exemplar attitude to American exceptionalism as articulated in the writing of Anne-Marie Slaughter.

Slaughter, in her thoughtful book, The Idea That Is America, revealed the paradox of American exceptionalism. A key element what makes America exceptional – its values – is actually universal. The American idea is great precisely because it is based on the essential notion of the universality of the human condition. 'To see it continue to flourish', argues Slaughter, 'we have to accept that it is no longer exclusively – or exceptionally – ours.' Expect to see this line of argument forwarded and sharpened at the Democratic National Convention this week.

This election offers a clear choice to Americans. It is a choice between two competing notions of American exceptionalism. Does America desire a leadership role under Romney, or a continued stewardship role under Obama? The times will suit one of these men and Americans will make that choice on 6 November. The world will be watching.

Photo courtesy of Wikipedia.