Just think about borrowing from China with dollars and paying them back with money worth half. There is a certain pain level they will reject. They stopped buying bonds when QE started and haven't really stepped up as they had before. For years now, the FED prints money to buy our own debt and then expands the Balance sheet. At some point trillions will be foisted on the market for someone to buy. I don't think there will be any takers. Eventually the interest rates will have to rise just to get a bite. Then we have the scenario I was speaking of. We CAN"T pay higher interest rates. As the rates rise, the debt rises, until it get's ridiculous like maybe 12 percent and the interest on the debt is waaaay more than the whole budget. We owe more but get less until it's upside down.
I don't know where the line is, but I know it's out there. As people say that's far enough, it quickly goes exponential. How long did it take for the markets to go from normal to 666 on the S&P? 5-6-700 points a day doesn't take long to go to zero.