The focus here is on the belief in American exceptionalism and its influence on U.S. foreign policy rather than directly addressing the question of whether U.S. foreign policy itself can be measured as exceptional. Indeed, Joseph Lepgold and Timothy McKeown have found little empirical evidence for claims that American foreign policy behavior is exceptional. Faults and blemishes riddle American history as much as that of any other nation. In foreign policy, the United States has a far from untarnished record. The colonization and expansion of the new nation were accompanied by the displacement or destruction of the indigenous population. Times of war have been plentiful, with the United States imposing its will on peoples in countries as distant as the Philippines and Vietnam, ordering the internment of large numbers of its own citizens, and committing atrocities like any other warfaring nation. Yet despite the abundance of evidence indicating that the United States is just as fallible as any other nation, there has remained throughout American history a strong belief that the United States is an exceptional nation, not only unique but also superior among nations. As Daniel Bell (1989) has argued, in the United States "there has always been a strong belief in American exceptionalism. From the start, Americans have believed that destiny has marked their country as different from others—that the United States is, in Lincoln's marvelous phrase, 'an almost chosen nation.'"
Lepgold and McKeown observe that American leaders make "unusual internal justifications" for their actions abroad, using "idiosyncratic symbols and metaphors … based on national self-image and values." It is the belief in American exceptionalism that most commonly provides these symbols and metaphors. Throughout American history, exceptionalist belief has framed the discourse of foreign policymaking by providing the underlying assumptions and terms of reference for foreign policy debate and conduct. Scholars disagree, however, over whether exceptionalism amounts to an ideology as such. Michael Hunt argues that the belief in "national greatness" is a central element of the ideology behind U.S. foreign policy. Alternatively, Siobhan McEvoy-Levy contends that exceptionalism amounts to a "paraideology" because its influence underwrites much of U.S. foreign policy but it does not have the coherence of a traditional ideology. John Dumbrell argues that American democratic liberalism is the ideology underpinning U.S. foreign policy but a belief in American exceptionalism is a central element of that ideology. It was Richard Hofstadter who observed, "It has been our fate as a nation not to have ideologies but to be one." The idea of "America" as a bastion of democracy, liberty, equality, individualism, and constitutionalism has given meaning and identity to millions of Americans throughout U.S. history (see Huntington, chapter 2). American nationalism, according to Hans Kohn, is not built on the usual elements of nationhood such as shared language, culture, common descent, or historical territory, but on "an idea which singled out the new nation among the nations of the earth." This idea was a "universal message" that American values and principles would benefit the whole of humankind. John Fousek agrees that this belief in the exceptionalism of the United States is a "core theme of American nationalism" that has been expressed most commonly in the "long-standing tradition of thought about American chosenness, mission, and destiny." Anders Stephanson has also shown how a "destinarian discourse" accompanied nineteenth-century American expansion and how it continued to shape the way Americans understood their place in the world during the twentieth century. The belief in American exceptionalism has been central to the formation of American national identity, and thus can be seen to have provided a significant part of the cultural and intellectual framework within which foreign policy has been made.