Just like with the banking system, the Fed's great white hope is that, given time, deleveraging in the private sector happens through retained earnings (i.e. increasing equity), rather than through asset disposals. Then the Fed balance sheet can gradually go away. Of course, that would require a) some aggregate demand somewhere (read China and rest of EM); and, b) that the US becomes a net exporter to places where this demand is to be found. Both adjustments are extremely painful and clearly have stalled recently (which is yet another bugbear to scare Big Ben).
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