Matt Yglesias starts but obviously I would go much further
Call this the foundational myth of modern central banking. Like all good myths, it doesn’t withstand even the tiniest amount of scrutiny. Consider Alan Greenspan, the most celebrated central banker of our era. To serve as a technocrat he must possess the techne, the knowledge of the discipline of economics that makes him credible as a High Priest of the economic order. And yet he is a man of flesh and blood. He cannot serenly segment his views of the monetary policy aspect of macroeconomics from his views of the rest. And he has a duty—a solumn duty—in his role as technocrat to do what’s right for the county. So in 2000 Greenspan tightens money, George W Bush wins the election, Greenspan explains that the budget surplus runs the risk of plunging the country into socialism and endorses the Bush tax cuts, in 2004 he maintains loose money, Bush wins again, and Bush sets about to try to privatize Social Security.
It would be scandalous to admit that such considerations entered into the mind of the Maestro, but it would be equally absurd for him to forget about them.
Ben Bernanke has said that he could not save Lehman because it would be have been in violation of the law. My response is that it is not his responsibility to enforce the law. It is his responsibility to safe guard the lives of millions of people.
When the Capitol Police haul him away in chains then his responsibility to prevent the Great Recession ends. Until that moment the choice not to act, is his choice alone.
The constitution is no shield.