It is not that the US has anything approaching a credible medium-term fiscal framework, but everyone else is in much worse shape.
This is silly. Germany is clearly not in a worse shape, for one. and Germany is the country that matters here. In the long run, we're all dead. John Maynard Keynes
In such a situation, we should expect that investors scramble for the safest assets available - "cash", which means short-term US government securities. It is not that the US has anything approaching a credible medium-term fiscal framework, but everyone else is in much worse shape.
After all, who cares about medium-term fiscal prospects when you're trading three-month bills? En un viejo país ineficiente, algo así como España entre dos guerras civiles, poseer una casa y poca hacienda y memoria ninguna. -- Gil de Biedma