“We presume … the central bank is unable or unwilling to provide additional stimulus ”
Shame on Larry Summers. He was the #1 econ person in the Administration through the critical time — with the levers of power in his hands — and by all accounts seen so far, his own and others, he did nothing whatsoever to make the Fed willing to provide more stimulus.
There were two empty seats to fill on the BoG and the Dems had a 60-seat filibuster-proof majority. He could have told Obama, “Fill those seats with appointees who will vote for additional stimulus, students of everything Bernanke said about Japan.” He could have made the Fed willing to provide more stimulus, it was his job to do that — but he did **nothing**. 
To me this is impossible to fathom. He didn’t want those seats filled? How does one avoid thinking he advised Obama to *not* fill those empty seats? Why?? (I don’t want to indulge my cynical imagination here). I don’t see how this is so different from if Truman had left two seats of the Joint Chiefs empty during the Korean war. How is this not dereliction of duty?
If the Fed was and is unwilling to provide enough stimulus during this recession, the #1 largest identifiable reason is: Larry Summers.
Now he writes: “We presume the central bank is unwilling to provide additional stimulus”. Please. Shame on Larry Summers.
FN:  Except write a planning memo to Obama saying there was only $300 billion of quality fiscal stimulus available “we do not believe it is feasible to design sensible proposals along these lines that go much beyond this total size”, with necessary amounts beyond that amount “not as effective as stimulus”. Now he is writing that deficits as large as one may desire are self-financing?
I’ve made the same argument in previous post, but nowhere near as effectively.
And here’s the commenter “Steve”:
DeSummers wrote: “We presume for the moment that monetary policy is constrained by the zero lower bound, and that the central bank is unable or unwilling to provide additional stimulus through quantitative easing or other means”
I feel like we are currently learning that Bernanke saying “we care about the dual mandate” and singing Kumbaya with the doves is even more powerful than QE.
Yes, we are to believe the Fed is out of ammo, yet somehow just the tiniest hint from Bernanke is enough to ignite a global equities rally. Here’s another great Steve comment:
Also, I think the DeSummers argument might be worse than you suggest. When they say “the central bank is unable or unwilling to provide additional stimulus through quantitative easing or OTHER MEANS” they affirmatively argue that the Fed *WILL* sabotage their stimulus. After all, one of the “OTHER MEANS” is a commitment to keep rates at or near zero even after the economy begins to recover and the Wicksellian rate goes positive.
They are assuming that the Fed will sabotage their stimulus, and ignoring the contradiction in the result!
Update: Tyler Cowen has a good post on the hysteresis issue, which is central to the DeLong and Summers model.