What's all this about American exceptionalism?

In this week's speech, President Obama said that the U.S. is exceptional and that's why we needed to punish Syria for use of chemical weapons.  In an op-ed today, Russia's Putin warns that it's dangerous to believe that one is exceptional in today's global environment.
http://www.huffingtonpost.com/2013/09/11/vladimir-putin-us-intervention_n_3910410.html?icid=maing-grid7|main5|dl1|sec1_lnk3%26pLid%3D373553

In the opening segmentof the first season of "The Newsroom," Aaron Sorkin has Jeff Daniels' character state that AMerica is no longer the greatest nation on the planet.
http://www.youtube.com/watch?v=JM3nvATF-U8

Sorkin/Daniels is probably right.

So where does this notion of American exceptionalism come from anyway?  Below are a few answers to this important question (important because this notion has gotten us into so much trouble):

http://en.wikipedia.org/wiki/American_exceptionalism

http://www.american.com/archive/2008/april-04-08/understanding-american-exceptionalism

http://iantyrrell.wordpress.com/papers-and-comments/

• American Exceptionalism
• The Reality Of American Exceptionalism