Ben Bernanke is losing one of his most valued lieutenants—Fed Governor Frederic Mishkin, who said on May 28 that he's leaving as of Aug. 31 to return to teaching at Columbia B-school. Mishkin, 57, who joined the Board of Governors in September, 2006, was early to see the danger to the economy from the housing downturn and credit crunch. Last Sept.1 he delivered a paper arguing that the Fed should chop rates aggressively in case of a then-hypothetical collapse in home prices. His departure leaves the Fed shorthanded because Democrats in Congress refuse to act on President George W. Bush's nominations.