The Treasury can temporarily delay buying new bonds by using social security's excess cash but Republicans will scream that the social security trust fund is being raided.

This fund is the excess of what my branch in which I am the manager made as profit during the last year.

At the same time the fund still has no clout over countries it does not lend to, even if their policies hurt the global economy (as the excess build-up of reserves, especially in China, surely did).