He is right you cannot call the debt, but you can sell it. China could unload the debt on the markets and force interest rates to jump. Not saying they would do this, but it can happen. During the financial collapse, Russia approached China about together dumping their US Debt all at once. This would have probably ended the US as we know it. China declined. At this point China and the US are joined at the hip, but that will not always be the case. Russians motive IMHO was to hurt the dollar enough to get it off oil and as the reserve currency.