From this piece by economist Thomas Sowell. You knew it but here it is again. Are you listening, President Obama and Peter Orszag?

Although the big stock market crash occurred in October 1929, unemployment never reached double digits in any of the next 12 months after that crash. Unemployment peaked at 9 percent, two months after the stock market crashed– and then began drifting generally downward over the next six months, falling to 6.3 percent by June 1930.
This was what happened in the market, before the federal government decided to “do something.”
What the government decided to do in June 1930– against the advice of literally a thousand economists, who took out newspaper ads warning against it– was impose higher tariffs, in order to save American jobs by reducing imported goods.
This was the first massive federal intervention to rescue the economy, under President Herbert Hoover, who took pride in being the first President of the United States to intervene to try to get the economy out of an economic downturn.
Within six months after this government intervention, unemployment shot up into double digits– and stayed in double digits in every month throughout the entire remainder of the decade of the 1930s, as the Roosevelt administration expanded federal intervention far beyond what Hoover had started.