• The current military establishment is exhausted and broke. A HUGE "investment" in armaments will be required if the U.S. is to maintain its ability to "lead" by military means. For example, most our F-15 air superiority fighters are all grounded because of structural failure, and the army is literally worn out--both in equipment terms and human terms.
  
• Energy crisis. The recent energy bill was a whitewash, and everybody in Washington knows it. Car fuel is one thing, but with heating bills exceeding $1000 per month in the Northeast, the problem is going to have to be solved.
  
• Global warming. While Bush and Cheney might not be willing to confront this problem, the next president will have to--given that his or her potential second term will overlap the start of the big and obviously undeniable environmental effects.
  
• Health care and social security. The baby boomers are just now starting to retire, and when they look at their first social security check and realize that they can't make their house, car, and medical payments, they will start to ask questions that have been ignored for 50 years.

The next decade is going to be interesting, that's for sure. I expect a Democrat to win, but it's really difficult to predict what they might do when confronted with so many big problems at the same time.