A complicated issue to be sure, with international ramifications that might not be obvious.
"If the government had not guaranteed the full payments of principal and interest on their paper, the foreign governments that own so much of it might have had to show losses on their dollar-denominated accounts. To say the least, this would make them reluctant to continue to finance our trade deficit, our wars and the strength (such as it is) of our dollar. Our interest rates, and not just for mortgages, would soar."
http://us.rd.yahoo.com/dailynews/fc/...ef=todayspaper