The Federal Reserve has as much to do with the Federal government as Federal Express.
Funny how many people don't realize that the Federal Reserve is a private cartel of banks which operates completely outside the control of the US government.
The Federal Reserve doesn't use taxpayer money to buy assets, they simply magic new money out of thin air and buy "stuff" with it. When the Federal Reserves says they are buying $85B worth of MBS each month it means they magically created $85B and exchange that newly created money for the MBS they are buying.
An idea of the scale of printing we are talking about ...
Yup $2T created out of think air and used to buy assets (to drive prices up and yields down).
they might actually... but not yet.