Obama Attends Nuclear Security Summit

President Obama followed the steps of his two most recent predecessors this weekend, with a trip to the Demilitarized Zone between North and South Korea. He's attending a summit aimed at reducing "vulnerable nuclear material" and keeping it out of the hands of terrorists. But, with 51 world leaders present, the talks are broader than the agenda. In a tough speech today, the President warned North Korea to back down on its nuclear program. Jim Walsh is a research associate at MIT's Security Studies Program.