U.S. debt is only about 100% of 1 year's GDP. If the government was a person (it's not, and it shouldn't act like one), that's about the maximum amount a person should take out on a loan for a house. So, I don't think it's catastrophic, yet. But, it's getting up there. The government must raise revenue and cut spending sometime soon in the future. That's the only way it could get out of the hole (that, and lessen the trade deficit). I'm no economist, but I think the government could raise a lot of revenue by raising taxes on imports, since our economy is extremely import heavy. If that discourages import consumption, then the trade deficit and employment improves, raising revenues. A win-win situation?
There are lots of ways the government can "get out of this hole", but they aren't likely to do any of them for exactly the same reason that they are in the hole.
The bond market will probably collapse in the next few years. This means print print print! because politicians don't want to stop giving handouts in exchange for votes.
I would be very surprised if the usd exists 10 years form now.