Democratic presidential candidate, Sen. Barack Obama, D-Ill., arrives at Midway International Airport in Chicago, Wednesday, July 16, 2008.
(AP Photo/Jae C. Hong)
Democratic presidential candidate Sen. Barack Obama, D-Ill. arrives at Purdue University in West Lafayette, Ind., Wednesday, July 16, 2008.
(AP Photo/Jae C. Hong)
Democratic presidential candidate, Sen. Barack Obama, D-Ill., shakes hands with former senator Sam Nunn following a panel discussion on national security at Purdue University in West Lafayette, Ind., Wednesday, July 16, 2008.
(AP Photo/Michael Conroy)
Democratic presidential candidate, Sen. Barack Obama, D-Ill., listens as Sen. Evan Bayh, D-Ind., talks during a panel discussion on national security at Purdue University in West Lafayette, Ind., Wednesday, July 16, 2008.
(AP Photo/Michael Conroy)
Democratic presidential candidate, Sen. Barack Obama, D-Ill., listens to panelists at a roundtable discussion on nuclear non-proliferation held at Purdue University in West Lafayette, Ind., Wednesday, July 16, 2008. Obama said Wednesday that two goals of his administration would be to secure all loose nuclear material during his first term and to ultimately rid the world of nuclear weapons.
(AP Photo/Jae C. Hong)
Democratic presidential candidate, Sen. Barack Obama, D-Ill., during a panel discussion on national security at Purdue University in West Lafayette, Ind., Wednesday, July 16, 2008. Obama said Wednesday that two goals of his administration would be to secure all loose nuclear material during his first term and to ultimately rid the world of nuclear weapons. (AP Photo/Michael Conroy)
Democratic presidential candidate, Sen. Barack Obama, D-Ill., second from left, talks with panelists at a roundtable discussion on nuclear non-proliferation held at Purdue University in West Lafayette, Ind., Wednesday, July 16, 2008. At left is Sen. Evan Bayh, D-Ind. Obama said Wednesday that two goals of his administration would be to secure all loose nuclear material during his first term and to ultimately rid the world of nuclear weapons.
(AP Photo/Jae C. Hong)
Democratic presidential candidate, Sen. Barack Obama, D-Ill., left, greets supporters after a roundtable discussion at Purdue University in West Lafayette, Ind., Wednesday, July 16, 2008. Obama said Wednesday that two goals of his administration would be to secure all loose nuclear material during his first term and to ultimately rid the world of nuclear weapons. (AP Photo/Jae C. Hong)