The retirement of Paul Krugman as a New York Times columnist is cause to lament — in part because it forecloses the prospect of a final reckoning from the Nobel laureate in respect of an honest dollar and the role of the Federal Reserve in America’s crisis of fiat money. For years, Mr. Krugman has served as a kind of bête noire of sound money advocates, mocking their warnings of inflation and denying gold’s role as the basis of monetary value.