Yet, that is not the main issue about this debate. The point is that ALL involved agree that the system has a natural (automatic) tendency to move back to the trend. Bordo refers nicely to Friedman's 'plucking' model. He reminds us, how it works:
"Friedman imagined the U.S. economy as a string attached to an upward sloping board, with the board representing the underlying long-run growth rate. A recession, in this view, was a downward pluck on the string; the recovery was when the string snapped back. The greater the pluck, the faster the bounce back to trend."So the deeper the recession was, the faster would the recovery be. In other words, for the GOP economists (Taylor in this case) Obama is
Krugman ideas are based on a recent paper on what he called the Fisher-Minsky-Koo model. Steve Keen has provided a full critique of a previous version here (h/t Lord Keynes who also provides an invaluable bibliography on debt deflations here). The essential point that generates an imperfection in the case of Krugman's model is that an external shock (a Wile E. Coyote moment in his terms, since agents finally notice the floor is gone) brings down the natural rate of interest, which becomes negative for a while (see my discussion on Krugman and the natural rate here). In that case, monetary stimulus is not capable of getting the economy naturally back on track, since the interest rate cannot fall below zero, and as a result agents cannot increase consumption enough to bring full employment automatically.
Hence, in the New Keynesian model of debt-deflation the change from more conventional neoclassical models is that they allow for a sudden (and exogenous) reduction in the debt limit that agents can borrow to reduce the natural rate. It's a financial shock (not a real one) that makes the rate of interest that would equilibrate investment with full employment savings (the inverse of consumption) negative. Agents suddenly understand that they would need a negative interest rate to satisfy their intertemporal consumption plans. From a post-Keynesian (I prefer classical-Keynesian but who cares), the problems are not related at all with the natural rate (yes the capital debates have shown that this makes no sense, where did I read that before?). So deleveraging has a direct effect on the ability of consumers to spend, and there would be no automatic bounce back if the equilibrium rate was not negative.
You may think it is a minor issue, and from a policy point of view it certainly the differences are minor. However, note that the New Keynesian version of the recovery suggests that markets are fundamentally, in the long run, efficient (again against logic and evidence) which is an essential totemic myth that they need to preserve.* And that has policy implications. Recoveries from financial crises are slow, as Krugman says, but not because the natural rate is negative. It is a political problem that involves class conflict. It is because agents that cannot consume out of wages (which have stagnated) cannot borrow themselves out of the crisis, and the federal government, the only one that can, will not do it for political reasons (to keep workers demands in line). That's why heterodox economists are not just for expansionary fiscal policy (and don't think that if the Fed signals more inflation investment confidence will pick up), but argue for higher wages, stronger unions, and debt relief.
* Let alone the funny thing that both sides in this dispute are basically arguing that the economy gravitates around a trend that is exogenous and attracts the actual economy (in a stronger or weaker way), and the way they actually measure the gravitational center (the natural trend) is by averaging the actual rates.
PS: And no, it's not a joke, they do actually sell that T-shirt!