US Democratic presidential candidate Senator Obama speaks during a campaign event at the National Constitution Center in Philadelphia

 
US Democratic presidential candidate Senator Obama speaks during a campaign event at the National Constitution Center in Philadelphia
US Democratic presidential candidate Senator Barack Obama (D-IL) speaks during a campaign event at the National Constitution Center in Philadelphia, Pennsylvania March 18, 2008. REUTERS/Tim Shaffer (UNITED STATES) US PRESIDENTIAL ELECTION CAMPAIGN 2008 (USA)