Absolute monarchs rule by whim. What they say goes. Even before Parliament existed, however, the barons of England insisted that monarchs rule in accordance with law, rather than mere executive whim or decree. King John (1199–1216) was a major offender against the rule of law. He arbitrarily increased taxes, abused the king’s court, mustered soldiers for military misadventures foreign and domestic, and hanged innocents in Wales. Things came to a head in 1215 at Runnymede. Faced with armed insurrection, John agreed to The Great Charter, which established the principle that the king is not a law unto himself; even the king must act through settled law to bind his subjects.

Thus began a centuries-long struggle between law and royal prerogative. The term prerogative refers to powers invested in the executive that are not governed by law. John Locke defined the term in his Second Treatise on Government: “This power to act according to discretion, for the public good, without the prescription of the law, and sometimes even against it, is that which is called prerogative.” The king’s prerogative powers included the veto, the pardon, the powers of war and peace, the power to create and fill public offices, and the power to dissolve the Parliament. All these he could do without the need for statutes passed by Parliament, and statutes passed by Parliament could not touch, limit, or regulate these prerogative powers.

Prerogative powers are not all inconsistent with constitutional government. Under the Constitution, for example, the president has certain defined prerogatives, such as the pardon power and the veto, which are committed to the president’s discretion. But much of constitutionalism consists of replacing prerogative with law. The framers of the U.S. Constitution carefully reflected on the various prerogative powers claimed or exercised by the English king and granted, denied, or limited those powers when creating the Article II executive.