The following is an neat chart showing the growth of US National Debt, GDP and debt held by the public. Most of the outstanding debt is held by the American public and not Chinese as commonly misunderstood. So the theory that China can crash the US economy by simply dumping their US treasury holdings is simply false.

Click to enlarge

Source: How I Learned to Stop Worrying and Understand U.S. Debt by Brian Levitt  Oppenheimer Funds