I rather like Lincoln's version of American Exceptionalism

Lincoln surely understood that slavery was morally wrong and that it stained the creation of the United States in the Revolution and in the Constitution. As I understand it, he also felt that the system of governance created by the founding fathers was such that the nation could evolve toward a still more perfect union than that established in 1789. Were the United States not to survive the Civil War, broken apart into slave and free states, the hope provided by the evolutionary improvement of the United States would have been denied to the world.

The question is whether 150 years after the Civil War the United States still is perfectible, and as such can continue to serve as an example for other nations.