Paul Krugman has some very sage advice for Barack Obama today:

F.D.R. wasn’t just reluctant to pursue an all-out fiscal expansion — he was eager to return to conservative budget principles. That eagerness almost destroyed his legacy. After winning a smashing election victory in 1936, the Roosevelt administration cut spending and raised taxes, precipitating an economic relapse that drove the unemployment rate back into double digits and led to a major defeat in the 1938 midterm elections.

What saved the economy, and the New Deal, was the enormous public works project known as World War II, which finally provided a fiscal stimulus adequate to the economy’s needs.

This history offers important lessons for the incoming administration.

The political lesson is that economic missteps can quickly undermine an electoral mandate. Democrats won big last week — but they won even bigger in 1936, only to see their gains evaporate after the recession of 1937-38. Americans don’t expect instant economic results from the incoming administration, but they do expect results, and Democrats’ euphoria will be short-lived if they don’t deliver an economic recovery.

The economic lesson is the importance of doing enough. F.D.R. thought he was being prudent by reining in his spending plans; in reality, he was taking big risks with the economy and with his legacy. My advice to the Obama people is to figure out how much help they think the economy needs, then add 50 percent. It’s much better, in a depressed economy, to err on the side of too much stimulus than on the side of too little.

The related point I'd make, which I think applies to the way the Bush administration has handled the financial crisis, is that policymakers often deal with unprecedented emergencies by going to the edge of what's acceptable by the standards of the moment, when in fact what's necessary is something well beyond that. The Great Depression demonstrated that you have to set aside existing norms when dealing with something potentially catastrophic, but that, psychologically (and politically), it's really hard to do.

--Noam Scheiber