WHEN SETTING up the checks and balances in the American constitution, the document’s authors knew they wanted the judiciary to be independent of the legislative and the executive branches. But who, then, would check the judges? One answer was that the president would be able to pardon criminals. This awesome power—to override a decision taken by the courts—should be used rarely, because it is at odds with democracy and judicial independence. If it seems a bit medieval to let one man dispense (and dispense with) justice in this way, that is because it is. In British law the “prerogative of mercy” can be traced back to the reign of King Ine of Wessex in the seventh century.