White House says nuclear-free world achievable

President Barack Obama's vision of a world without nuclear arms is an achievable goal and the president will pursue it with an eye on the lessons learned from four decades of difficult diplomacy, the White House said Saturday. The comments by Denis McDonough, deputy national security adviser for strategic communications, came aboard Air Force One on the eve of the president's speech in Prague on nonproliferation. McDonough said the twin issues of nuclear disarmament and nonproliferation provide the United States and its allies with a powerful argument to ensure that Iran does not develop nuclear weapons. The challenge is to maintain an effective deterrent as long as there's any threat in the world, McDonough told reporters.