The unitary executive theory is a theory of United States constitutional law which holds that the (US President) possesses the power to control the entire executive branch. The doctrine is rooted in Article Two of the US Constitution, which vests "the executive power" of the United States in the President. Although that general principle is widely accepted, there is disagreement about the strength and scope of the doctrine. It can be said that some favor a "strongly unitary" executive, while others favor a "weakly unitary" executive. The former group argue, for example, that US Congress's power to interfere with intra-executive decision-making (such as firing executive branch officials) is limited, and that the President can control policy-making by all executive agencies within the limits set for those agencies by Congress. Still others agree that the Constitution requires a unitary executive, but believe this to be harmful, and propose its abolition by constitutional amendment. Plural executives exist in several states where, in contrast to the federal government, executive officers such as lieutenant governor, attorney general, comptroller, secretary of state, and others, are elected independently of the state's governor. The Executive Branch of the Texan state government is a textbook example of this type of executive structure. Another type of plural executive, used in Japan, Israel, and Sweden, though not in any US state, is one in which a collegial body composes the executive branch – however, that collegial body does not comprise multiple members elected in elections, but is rather more akin to the US Cabinet or UK Cabinet in formation and structure. https://en.wikipedia.org/wiki/Unitary_executive_theory
Contrary to claims of some authors, the first administration to make explicit reference to the "Unitary Executive" was not that of President George W. Bush. For example, in 1987, Ronald Reagan issued a signing statement that declared: "If this provision were interpreted otherwise, so as to require the President to follow the orders of a subordinate, it would plainly constitute an unconstitutional infringement of the President's authority as head of a unitary executive branch."
The George W. Bush administration made the Unitary Executive Theory a common feature of signing statements. For example, Bush once wrote in a signing statement that he would, "construe Title X in Division A of the Act, relating to detainees, in a manner consistent with the constitutional authority of the President to supervise the unitary executive branch and as Commander in Chief and consistent with the constitutional limitations on the judicial power." Critics acknowledge that part of the President's duty is to "interpret what is, and is not constitutional, at least when overseeing the actions of executive agencies," but critics accused Bush of overstepping that duty by his perceived willingness to overrule US courts.