This chart and the commentary both come from FT Alphaville:
A look at the Fed’s balance sheet currently will tell you it’s very much in the business of supporting liquidity/prices in assets other than Treasuries. The graph below is a month old, but the point still holds:
The purple and red lines show the declining number of treasurys and bills held by the Fed, replaced by securities accepted under the new open market liquidity ops (green and light blue lines).
Of course, all this implies a rather long term dependence by banks on the Fed’s new auction facilities and a complete transformation of the Fed’s role in the market.
Source
The parabolic Fed: divorcing monetary policy from money – FT Alphaville