Larry Summers is becoming more and more worried that secular stagnation is real:
Convinced of the Secular Stagnation Hypothesis: Foreign Affairs has just published my latest on the secular stagnation hypothesis. I am increasingly convinced that it captures what is going on in the industrialized world and that the risks of long term weakness on the current policy path are growing.
Unfortunately since I put forward the argument in late 2013, the data have been all too supportive. Despite monetary policy being much more expansionary than was expected and medium term interest rates falling rapidly, growth and inflation throughout the industrial world have been much lower than anticipated. This is exactly what one would expect if structural factors were increasing saving propensities relative to investment propensities. ...
If I am right in these judgments, monetary policy should now be focused on avoiding an economic slowdown and preparations should be starting with respect to the rapid application of fiscal policy. The focus of global coordination should shift from clichés about structural reform and budget consolidation to assuring an adequate level of global demand. And policymakers should be considering the radical steps that may be necessary if the US or global economy goes into recession.
Of course, real time economic theorizing is problematic and I cannot be certain that I am reading the current situation accurately. If the Fed succeeds in significantly raising rates over the next two years without a growth slowdown and if inflation accelerates to 2 percent, I will conclude that the secular stagnation hypothesis was overly alarmist in confusing cyclical elements with long term problems. If on the other hand, the economy turns down even at current interest rates, secular stagnation will have to be taken more seriously by policymakers than is currently the case.