He suddenly dies in office and Sarah Palin become president and nukes Russia, starting WWIII.
Just kidding

Probably they will impeach Sarah Palin so some trash does not start if McCain dies in office, since she knows nothing about how to run a country. I can run a country far better than she can and I haven't graduated from college yet. Then possibly riots would break out, because people would think Obama should have won the election if something like the Bush?Al Gore situation. That's what I think is possible