Bailouts, infrastructure and financial stimulus will require big money during a deepening recession. Barack Obama also needs to worry about defense. The US spends almost as much on defense as the rest of the world combined, and more than any time since World War II. But it's stretched too thin to cover both Iraq and Afghanistan. Potential new threats might come from Iran, North Korea, Russia or China, from unstable countries like Somalia or from Pakistan with nuclear arms, not to mention terrorists of increasing sophistication. Will future threats be from conventional warfare or counterinsurgency? Will they require more troops or more high-tech equipment for smaller forces? We look at some of the toughest questions the next president will have to answer.