President Obama joined a band of blues all-stars including Mick Jagger, B.B. King, Booker T. Jones and Buddy Guy for a rendition of the standard "Sweet Home Chicago" last night at a concert in the East Room of the White House celebrating the blues. Obama, who recently impressed music fans by singing a few lines from Al Green's classic "Let's Stay Together" at an event in Harlem, was just as smooth in this impromptu performance, which occurred when the musicians urged the President to pick up a microphone.