While I don't think it's outside of the realm of possibility that the US as we know it would crumble, I don't think it's happening yet. This is nothing new really. We had Vietanm, which in a lot of ways was worse than Afghanistan/Iraq (though shorter). We've had recessions/depressions before and come out of it stronger. I'm not a huge politics buff, but have we ever had a government as polarized as we do today? That's the one thing that really worries me.
Interesting speculation might be how the US would break up and restructure were it to fall apart. I think it would basically be a split between the liberal (New England, upper Midwest, West) and conservative (south, lower Midwest, maybe the rockies region) states. Perhaps with Texas becoming it's own country. Any thoughts?