In his excellent book Liberalism and its Discontents, historian Alan Brinkley recounts that when Alvin Hansen, FDR's influential economic advisor, was asked (in 1940!) whether the "basic principle of the New Deal" was "economically sound," Hansen responded, "I really do not know what the basic principle of the New Deal is."
Today liberals denounce conservative efforts to "repeal" the New Deal. But in fact most of the New Deal was repealed a long time ago, much of it by FDR himself when it failed. And what remains is a mixed bunch. The reforms of the financial markets, speaking broadly, are worth keeping. There's no reason to nuke the Tennessee Valley Authority. But who misses that spectacular failure, the NRA? Who wants to see dry cleaners thrown in jail for not charging what federal bureaucrats claim is a fair price? And who wants to see millions of pigs slaughtered by the feds just to prop up pork prices?
If the measure of the New Deal is whether or not it boosted confidence in activist government, it was a huge success. If you judge it by whether or not it ended the Depression - it's intended purpose - the historical judgment is in: It was a miserable failure.
It did calm a nation that was, in the words of one publication at the time, wracked by "fear, bordering on panic, loss of faith in everything, our fellowmen, our institutions, private and government."
Calming such panic is worthwhile. But why should we be forever wedded to decisions made amid fear and panic? "Take a method and try it," FDR was fond of saying. "If it fails, admit it frankly and try another. But above all try something." The only coherent policy Roosevelt subscribed to was "bold, persistent experimentation."
Even if many of Roosevelt's policies were horribly misguided at the time - like his early decisions to slash government pay and veterans' benefits - experimentalism made a certain intuitive sense when the modern economy didn't seem to operate according to 19th-century laissez-faire rules. But since the 1930s the industrialized world has experimented a great deal with the New Deal model, while we've only been applying free-market solutions for the modern economy since the mid-1970s, to considerable success.
Today, liberals and conservatives alike favor experimentation to a certain extent. One side believes that some great panacea, untried by the welfare states of Europe, is around the corner. The other side believes the great answers aren't in a bureaucrat's filing cabinet, but in an entrepreneur's imagination. Which sort of experimentation would FDR favor? That's easy: Who cares?