Robert Barro says two things:
Free exchange | The Economist: My conclusion is that QE2 may be a short-term expansionary force, thereby lessening concerns about deflation. However, the Treasury can produce identical effects by changing the maturity structure of its outstanding debts.
The downside of QE2 is that it intensifies the problems of an exit strategy aimed at avoiding the inflationary consequences of the Fed’s vast monetary expansion.
Would we say that a change by the Treasury in the maturity of its outstanding debt intensifies the problems of devising an exit strategy for unwinding the Federal Reserve's vast monetary expansion when it is appropriate?
I do not think we would. The problems of the Federal Reserve exit strategy are there, and they remain unchanged no matter what the Treasury does with the maturity structure of its debt.
So how is it that QE can (a) be identical to a Treasury shift in maturity structure, and yet (b) intensify problems of unwinding monetary expansion?