Pennsylvania Presidential Primary (27 images)

Democratic presidential hopeful Sen. Barack Obama addresses supporters at the Peterson Event Center in the Oakland section of Pittsburgh on April 21, 2008, the eve of the Pennsylvania Primary election. (UPI Photo/Archie Carpenter)

Democratic presidential candidate Sen. Hillary Clinton talk to supporters in Market Square in Pittsburgh Pennsylvania on April 21, 2008 (UPI Photo/Stephen Gross)

Democratic presidential candidate Sen. Hillary Clinton talk to supporters in Market Square in Pittsburgh, Pennsylvania on April 21, 2008 (UPI Photo/Stephen Gross)

Democratic presidential hopeful Sen. Barack Obama addresses supporters at the Peterson Event Center in the Oakland section of Pittsburgh on April 21, 2008, the eve of the Pennsylvania Primary election. (UPI Photo/Archie Carpenter)