In 1940, when Alvin Hansen, an influential economic adviser to the president, was asked whether "the basic principle of the New Deal" was "economically sound," he responded, "I really do not know what the basic principle of the New Deal is."
In fact, when it's convenient, liberals usually brag about the fact that it wasn't a coherent plan at all. They praise FDR's "bold experimentation" and "pragmatic trial and error" on a colossal scale. In his famous Oglethorpe University commencement speech in May 1932, FDR himself said some of his proposed program wouldn't work—and he was right. In a recent interview with 60 Minutes, Obama echoed this argument. "What you see in FDR that I hope my team can emulate is not always getting it right, but projecting a sense of confidence and a willingness to try things and experiment in order to get people working again."
On this point Amity Shlaes is surely onto something when she argues that bold experimentation fosters an atmosphere of uncertainty—"What's FDR going to try next?!"; "What's Obama up to now?!"—and uncertainty is not necessarily good for economic growth or employment.
Yet, again, from the liberal perspective, this misses the point entirely. Some of the New Deal surely helped, and much of it definitely hurt, they might grudgingly concede; but to get mired in such questions is to overlook the true meaning and majesty of it all. This was the first time while the country was not at war that the American people gave war powers to liberals to do whatever they thought best. That's what liberals love about the New Deal, and that's the real reason they want to bring it back.