Prerogative power

Prerogative power is a legal doctrine that originated in England, giving the sovereign the right to operate in a supra-legal manner if he determined it was in the supreme national interest, typically in the common defense. Historically, the medieval monarchy was both feudal lord and head of the kingdom. As such, the King had powers accounted for by the need to preserve the realm against external foes and an ‘undefined residue of power which he might use for the public good’. He could exercise the ‘royal prerogative’ and impose his will in respect of decision-making. Variations of that authority appear to have been resisted by the Framers of the U.S. Constitution, but, certainly from the Truman Administration on and arguably by Franklin D. Roosevelt, have been used by Presidents of the United States. In the U.S. context, as the legal concept developed, it tended to be called the Unitary executive theory.

United Kingdom
In practice, the UK Crown only has limited use of the prerogative; its use has devolved to Ministerial level. The three main uses, some of which have not been exercised in centuries, are:
 * 1) appointment of a Prime Minister
 * 2) dissolution of Parliament
 * 3) giving of royal assent to legislation, in 1708 Queen Anne was the last sovereign to refuse royal assent to a bill passed by Parliament. Additionally, no monarchs since the sixteenth century have signed Bills themselves and Queen Victoria last gave verbal assent in 1854.

United States
As used in American constitutional discourse, the principle comes from John Locke. While Locke argued, in the Second Treatise of Civil Government that the "first and fundamental law is the establishment of the legislative power." This principle is a reason that Article I of the U.S. Constitution deals with the Congress, not the Presidency. Locke, however, agreed there are many things "which the law can by no means provide for." Walter Berns interpreted this as "The law cannot "foresee" events, for example, nor can it act with dispatch or with the appropriate subtlety required when dealing with foreign powers. Nor, as we know very well indeed, can a legislative body preserve secrecy." Locke, in the same writing, continued that such events should be left to "the discretion of him who has the executive power." It is in this context that he first spoke of the "prerogative": the "power to act according to discretion, for the public good without the prescription of the law, and sometimes even against it." He concluded by saying "prerogative is nothing but the power of doing public good without a rule" (italics in the original).

There is considerable argument, however, if the Framers intended to give any Presidential prerogative power. Alexander Hamilton wrote of "presidential unity" in Federalist 70, the document perhaps most frequently cited by supporters of the unitary theory. Charlie Savage interprets this as simply meaning the President need not first reach a consensus within the Executive, as was, for example, the case in the Second World War Japanese Cabinet. Federalist 69, however, said that while the President, as did the British King, would oversee the military, he would be "first general", with much less power than a king, for the power to create armies and declare war is given to the Congress. The first clear major war started on sole Presidential authority was the Korean War; the need to respond quickly to nuclear threat caused further delegation during the Cold War, but Congress began to challenge the authority after the Vietnam War with the War Powers Resolution.