Debt is a meaningless figure unless it's stated in terms of GDP.

Here's an example.

Let's say i'm $5,000,000 in personal debt. You might think my situation is hopeless, that i'm about to have everything reposessed, i'm about to see my house go into foreclosure, and declaring bankruptcy is imminent.

Surprise! $5M is a a chicken's fart worth of debt if I have $50,000,000,000 in the bank. This analogy is true of the US economy. We have ample ability to sustain that debt load. It helps when the world depends on your currency. And you're investing trillions in other countries. And have a crapload of assets. And exports out the wazoo.

The US is a very, very wealthy nation. The #1 economy in the world. Our debt can be in the trillions, and that be completely fine, as long as our growth of bad debt is not outpacing our ability to sustain it. We have enormous currency reserves, to top it off, and 60% of the world's money is dollar-backed..Our debt load can be 100% of GDP, and still be fine numerically. It would mean 0% growth, but, with equal money going out and coming in, everything that needs to be paid is still getting paid.

Citation:

http://en.wikipedia.org/wiki/Economy_of_the_United_States