Its essential contribution to modern political thought lies in Machiavelli's assertion of the then revolutionary idea that theological and moral imperatives have no place in the political arena. "It must be understood," Machiavelli avers, "that a prince ... cannot observe all of those virtues for which men are reputed good, because it is often necessary to act against mercy, against faith, against humanity, against frankness, against religion, in order to preserve the state." With just a little imagination, readers can discern parallels between a 16th-century principality and a 20th-century presidency.