still could pay interest on the debt

If no agreement reached default does not mean they could not service the debt if they wanted to, which is the bottom line most vitally important event. Of course there is always a time limit on everything. Eventually the interest on the debt climbs so high everything we could borrow would go to payment of the debt. That then is ground zero. Someday the money is going to have to be to be devalued, that is a mathematically done deal at this point. It all depends now on perception to predict the actual blow out point. The country is sinking under its own weight. All roads led to Rome, just as they now they lead to the US. When it all happens the pot will already been boiling for some time.