President Obama talks with host David Letterman on the set of "Late Show With David Letterman" at the Ed Sullivan Theater in New York on Tuesday, Sept. 18, 2012. (AP Photo/Carolyn Kaster)

Photo by: Carolyn Kaster

President Obama talks with host David Letterman on the set of "Late Show With David Letterman" at the Ed Sullivan Theater in New York on Tuesday, Sept. 18, 2012. (AP Photo/Carolyn Kaster)