What caused the Great Depression? There are plenty of theories and arguments out there, and I don’t plan to review them. But a new one (at least new to me) is contained in a paper by Lee Ohanian, a U.C.L.A. economist, that was released today by the National Bureau of Economic Research. He blames Herbert Hoover. That is not exactly original; the Democrats ran against Hoover for a generation after he left office, much as some would now like to run against George W. Bush. But his criticism is that Hoover was too kind to workers, which is not exactly...