Four really, really bad scenarios - Eamon Javers - Politico.com

The Bait Effect: A terrorist attack takes advantage of the economic crisis to have a "multiplier" effect.

The China Syndrome: China dumps its near trillion dollars in U.S. bonds and other obligations and pulls the rug under Our economy... and maybe theirs as well. But as they say in chess, it's not what you do, but what you can do that influences the game.

The Existential Crash: The U.S. of part of A. staggers, stumbles, pulls its focus inward to keep from reeling into a coma and the rest of the world slides into a higher level of chaos.

The Alternate-Dollar Nightmare: Simple: The moment a currency appears that has the power to attract investment away from the dollar, the dollar's toast. (It's worth that now.) 

But, as the article points out, who would you rather be, the U.S. or some other country? That's where the opportunity--and responsibility--lie.