Play of the Day: Letterman traces source of earthquake to 'Chris Christie's aerobics class'

David Letterman had some fun with reaction to the earthquake that shook the East Coast on Tuesday, joking that New York City Major Michael Bloomberg was found "standing under his desk" at city hall.

"They traced the epicenter of the earthquake to Gov. Chris Christie's aerobics class," Letterman said.

Today's Must See Moment -- Fast forward to 2:06 where MSNBC's Rachel Maddow tells Letterman how the country would be different if Sen. John McCain were president.