The US government must raise its debt limit or it will technically default which may cause the worlds markets to react and may cause a massive double dip.  There are many outcomes to this, one is that the stock market might crash again, the bond market may get cooked and bond holders will take a huge hit or the US dollar might crash (afterward it will do a bounce).

The best case is that stock market will crash but the US dollar will be steady, the worst case scenario is massive inflation (1970's style or maybe even hyperinflation which would be a total currency collapse. In the long term the US goverment must also raise the age for SS and cut spending across the board or the US government will enter hyperinflation. Right now the US government is borrowing 40% more then total tax receipts which is the turning point according to a Swiss Economist Peter Bernholz. 

VIDEO ON DEFAULT HERE

http://www.youtube.com/watch?v=cEB-bchEfzo