'American Exceptionalism:' Myth or Reality?

Almost since the revolution that created the United States, Americans have considered themselves as a nation apart. "American Exceptionalism" is now a standard theme for Democrats and Republicans. With economic and military expansion, world leadership has been seen as an obligation. But, for all its contributions to human progress, does the US really behave that much better than other nations? Are there dangers in that kind of thinking? Should the US recognize its weaknesses as well as its strengths or, if it focuses too much on past mistakes, will it fail to take the actions required for the future? We hear an argument crucial to the assumptions that dictate national policy. How does America look to the rest of the world?