"Unitary Executive Theory" is perhaps a term of art, but it is one that captures a school of constitutional thought, according to which the vesting clause of Article II, section I - which declares that the executive power shall be vested in a President of the United States of America - confers vast unenumerated powers upon the executive branch, and, according to certain of its theoreticians, plenary powers, such that the Constitution is read to impose strictures upon the courts, and upon the Congress, yet none upon the executive. It is the ideology of the President as the Decider, the mystagogue who, by invocation of 'national security', or 'emergency powers', decrees exceptions to the law - himself as an exception, to whom the law does not apply, as the invocation renders him the sole judge of his own determinations, and exceptions to the process of law, by which persons become simultaneously entitled and not entitled to legal protections and procedures, at his discretion. It is the legal philosophy undergirding the infamous torture memorandums of John Yoo, war criminal, in defense of which he averred that the president could order a child's testicles to be crushed, if by doing so, a terrorist might be 'encouraged' to divulge information.
Alas, for such sibyls hymning the imperium and its pretenses of unlimited power, the foundation of this doctrine in the Constitution is negligible. According to Gene Healy, author of The Cult of the Presidency,
But there are a number of hurdles to jump before one can conclude that the president has plenary power over foreign affairs - and domestic affairs as well, to the extent that his actions can plausibly be characterized as serving the end of national security. First one has to establish that the constitutional text indicates a general grant of power to the executive - that the president's powers go beyond those specifically enumerated in Sections 2 and 3 of Article II. Second, if "the executive Power" is a general grant of power, one still has to unpack what that power contains. What is "the whole thing"? Is it broad enough, as many unitarians suggest, to allow domestic surveillance and imprisonment without trial, so long as those activities are incident to the president's wartime goals?
Is the vesting clause, namely, the first sentence of Article II, a general grant of "executive" power? If it is, then the enumeration of specific executive powers that follows in Article II, Sections 2 and 3, is largely redundant. If the president has "the whole thing", whatever it is, surely it must be broad enough to include requiring "the Opinion, in writing," of the heads of each executive department, ro to allow him to "receive Ambassadors." (Emphasis mine.)
Further, if the vesting clause is a general grant of power - a font of significant "residual" authority not contained in the specifically enumerated Article II powers - it's surprising that so little of the discussion at the Philadelphia Convention, in the Federalist, and at the ratification conventions appears to reflect that. It's worth noting that, for all the emphasis unitarians put on the difference in wording between the introductory clauses of Article I (applicable to Congress) and Article II (applicable to the president), at the convention, few, if any, of the delegates noted the difference. The "herein granted" language was added to Article I by the Committee of Style, which had no official power to make substantive changes. At no point during the Constitutional Convention did any participant argue that the vesting clause constituted a general grant of power. (Emphasis mine)
Hamilton's defense of the office in the Federalist centers on the powers listed in Article II, Sections 2 and 3, rather than addressing the clause that unitarians claim would have been understood by 18th-century Americans to include broad powers over war and peace. Historian Jack Rakove notes that the proponents of the vesting clause thesis have failed to provide evidence that any participant in the extensive debates over the Constitution's ratification understood the clause that way:
If we know anything about the public discussions of 1787-1788, it was that when it came to identifying potential sources of tyranny and misrule in the Constitution's numerous clauses, Anti-Federalists wrote with promiscuous abandon. Here is one case where the inability to produce a single source positively falsifies the claim being made
Finally, the vesting clause thesis - at least in its broadest incarnations - fits uneasily with the principle that our Constitution is one of enumerated, and thus limited, powers. Madison's assurance in Federalist No. 45 that "the powers delegated by the proposed Constitution to the federal government are few and defined," was also the key argument the Federalists presented against a Bill of Rights. Since no power had been granted that could threaten private rights, Hamilton asked, "why declare that things shall not be done which there is no power to do?"
Unitary executive theory not only facilitates the subversion of duly-enacted laws and the checks and balances of the constitutional order, and not only finds employment as a legitimating myth for war crimes and other injustices, it is simply, nakedly, unconstitutional. The Constitution does not provide for the obscene secret supplement to itself, by which its provisions may be disregarded where this suits the executive. The veritable conditions of its ratification render this constitutional theory inconsistent with any plausible doctrine of original intent. It is a more contemporary innovation and distortion, and if it is one made seemingly persuasive on account of modern myths of the activist presidency, that is a failing of the American people, who have embraced such fables. We cannot, however, use the Constitution as a fig leaf.