Add to the above, that the Fed has to find the financing for Congress’s deficit spending. That is finance either of two ways:
1) Printing money which increases money supply and is highly inflationary.
2) Issuing treasuries. The yield (fed rate) on the treasuries has to be high enough for people/institutions/countries to want to by it. Too low a rate, and no buyers. This means that the fed may not be able to lower interest rates very far.
