The phrase "unitary executive" was discussed as early as the Philadelphia Convention in 1787, referring mainly to having a single individual fill the office of President, as proposed in the Virginia Plan. The alternative was to have several executives or an executive council, as proposed in the New Jersey Planand as promoted by Elbridge Gerry, Edmund Randolph, and George Mason.^[6][7]

At the Pennsylvania ratifying convention in 1787, James Wilson emphasized the advantages of a single chief executive, including greater accountability, vigor, decisiveness, and responsibility:

[T]he executive authority is one. By this means we obtain very important advantages. We may discover from history, from reason, and from experience, the security which this furnishes. The executive power is better to be trusted when it has no screen. Sir, we have a responsibility in the person of our President; he cannot act improperly, and hide either his negligence or inattention; he cannot roll upon any other person the weight of his criminality; no appointment can take place without his nomination; and he is responsible for every nomination he makes. We secure vigor. We well know what numerous executives are. We know there is neither vigor, decision, nor responsibility, in them. Add to all this, that officer is placed high, and is possessed of power far from being contemptible; yet not a single privilege is annexed to his character; far from being above the laws, he is amenable to them in his private character as a citizen, and in his public character by impeachment.^[8]

In 1788, the letters of the Federal Farmer were published, generally considered among the most astute of Anti-Federalist writings. The pseudonymousFederal Farmer defended the proposed unitary executive, arguing that "a single man seems to be peculiarly well circumstanced to superintend the execution of laws with discernment and decision, with promptitude and uniformity."^[9]

Meanwhile, Federalists such as James Madison were emphasizing an additional advantage of a unitary executive. In Federalist No. 51, he wrote that an undivided executive would strengthen the ability of the executive to resist encroachments by the legislature: “As the weight of the legislative authority requires that it should be thus divided [into branches], the weakness of the executive may require, on the other hand, that it should be fortified.”^[10]

Alexander Hamilton later pointed out that the Constitution grants executive power and legislative power in different ways, with the legislative powers of Congress being expressly limited to what is "herein granted," unlike executive powers which are not expressly limited by an enumeration. Hamilton wrote:

In the article which gives the legislative powers of the government, the expressions are "All legislative powers herein granted shall be vested in a congress of the United States." In that which grants the executive power, the expressions are "The executive power shall be vested in a President of the United States." The enumeration ought therefore to be considered, as intended merely to specify the principal articles implied in the definition of executive power....^[11]

In other words, the principle of expressio unius may be more applicable as a limitation upon congressional power than upon executive power. According to Hamilton, the unenumerated executive powers that are vested solely in the President "flow from the general grant of that power, interpreted in conformity with other parts of the Constitution, and with the principles of free government."^[11]

Those other parts of the Constitution include the extensive powers granted to Congress. Article I of the Constitution gives Congress the exclusive power to make laws, which the President then must execute, provided that those laws are constitutional. Article I, Section 8, clause 18 of the Constitution known as the Necessary and Proper Clause grants Congress the power to "make all Laws which shall be necessary and proper for carrying into Execution all Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof". The Constitution also grants Congress power "To make Rules for the Government and Regulation of the land and naval Forces." The theory of the unitary executive can only be legitimate insofar as it allows Congress to wield its constitutional powers while ensuring that the President can do the same.