I thought a bit about American Exceptionalism.
First, there is a difference between nationalism -- in a sense of patriotism, being proud for your nation and its accomplishments -- and exceptionalism. Patriotism identifies a person and his/her country -- and thus should be taught, cultivated, and encouraged.
On the other hand, IMHO, exceptionalism implies entitlement. In a sense that someone does not need to follow general rules and principles. If one defines the whole nation that is above the rules of the world one can quickly get to Nazism. This is what happened to Germany (and Italy) in the early 20th century.
Moreover, according to the Declaration of Independence "all men are created equal", which excludes exceptionism as a basis on which this country is built.