US Democratic presidential candidate Senator Barack Obama (D-IL) (R) talks with students from Holy Cross School in Garrett Park, Maryland, as he departs after a vote at the US Capitol in Washington, May 13, 2008. Democratic Democratic presidential hopeful Sen. Barack Obama, D-Ill., left, greets Sen. John Kerry, D-Mass., as he leaves the Russell Senate Office Building after a workout, Tuesday, May 13, 2008, on Capitol Hill in Washington. Democratic presidential candidate Senator Barack Obama (D-IL) throws a bottle of water to the crowd during a campaign stop in Louisville, Kentucky, May 12, 2008. Democratic presidential hopeful, Sen. Barack Obama,...