The way they would pull the plug is by not buying anymore T-bills at all (1Yr, 2Yr, 3Yr, 5Yr, etc...).
They would then get rid of all their US dollars by buying gold or silver or some other currency, thereby flooding the market with US Dollars and not underwriting the US's debt anymore by not buying their bonds.
This will then leave the US with no more money to finance its needs. They will need to buy their own debt, which is already occuring. By buying their own bonds they are in effect printing money (Electronically).
As for the US defaulting, it is very unlikely to happen because their dollar is the reserve currency of the world. They owe the Chinese US dollars, not gold or silver or anything else. Whether the Chinese like it or not they will get paid in US dollars and so will every other creditor. If your currency is the reserve currency of the world you cannot default on your debt because you just create the money required to pay back your debts. Its that simple.
Its just like the Weimar Republic but on a global scale!!!
