I think the situation is actually rather more dire than most commentators are making it out to be. The biggest problem is not a "credit crunch". It's that the US has basically had zero growth in real industries (eg. not finance or real estate) in 10 years, and there's no sign that that will turn around any time in the future. The government has done nothing in terms of investing in education or research or improving the business environment for companies that could actually help us. And now it no longer has the cash to do so.
There are various nightmare scenarios that I don't think are terribly far fetched. They mainly involve the world getting fed up with our financial crisis and turning to other currencies and treasuries. OPEC could switch to pricing oil in Euros. China might stop investing in treasuries, and perhaps worse could let the Yuan float and stop buying dollars at a fixed rate. Those things in combination could lead to a huge plummet in the dollar.
The US government is absolutely fucked and I don't see how we're going to get out of it. We've got a huge defecit, taxes are cut and need to be raised, the burden of medicare and social security is ever increasing, and we've already been cheating our future by already not putting the spending we desperately need into things like infrastructure, polluting less, etc. bills that we'll have to pay.
Now I don't think we're going to be poor any time soon, but we might have to start living like Europeans or something. You know, consuming less, driving smaller cars, turning off lights when not in the room, running the heat and AC less, wearing clothes for more than 6 months, buying condos or duplexes instead of giant houses in the suburbs. The horror!!!
I actually think the end result may be that the Republicans get their wish and one of the major pillars of our government might be demolished. Something like Social Security or Medicare. (of course they would never stop funding their buddies in defence). Cutting either of those entitlements is politically impossible in normal situations, but if you manage to completely bankrupt the government there might be no choice.