OT Medchal, wrt US debt
The US debt will be considered risk free from a default perspective as long as it is denominated only in US dollars. That's just one of those facts. Worst case is the Fed just uses it's magic checkbook.
It is true that if the US starts having to monetize the debt, the dollar would become inflated and thus the value of the debt would decrease, but we were talking defaults and credit ratings, not exchange rates.