George W. Bush took a dim view of treaties designed to ban the testing of nuclear bombs and limit proliferation of materials and technology. Today, Barack Obama made history as the first American president to chair a meeting of the UN Security Council and in persuading all 15 members — represented by their heads of state — to approve a resolution including steps toward what the President calls "a world without nuclear weapons." But critics say he's "overselling" provisions that can't be verified and which won't make the world any safer from rogue states or international terrorists. What will it mean for Iran and North Korea? Will it help persuade the US Senate to ratify the comprehensive test ban treaty it rejected in 1999?