Mainstream economists hold sacred the notion that central banks must be shielded from political influence. The U.S. Federal Reserve’s fundamental job is to set interest rates at the optimal level to keep employment high and inflation low. This often requires inflicting short-term pain—such as steeper borrowing costs or temporarily higher unemployment—to avoid even more disastrous outcomes in the long term. Elected officials, the thinking goes, don’t have that kind of patience. With an eye...