[SeeSharp]

China calls in the US debt.

China cannot "call in" US debt. The most they can do is dump US treasuries on the open market, which would raise the interest rate on new treasury issues raising the US government's cost of borrowing.

[Daus]

The most they can do is dump US treasuries on the open market

Well, and stop buying our NEW debt we keep generating. Since we operate a ponzi scheme these days, the lack of new money would be problematic.