The Framers fittingly placed the Oath of Office Clause between preceding clauses that set forth the organization of the executive department and succeeding clauses that specify the contours of the president’s executive power. The president takes the oath after he is to assume the office, but importantly before he executes it. The location and phrasing of the clause strongly suggest that it is not empowering, but that it is limiting—the clause limits how the president’s “executive power” is to be exercised.

The clause is one of several that employ the oath concept, but it is the only clause that specifies the actual oath language for a constitutional actor. The clause does not specify who shall administer the oath, though it has been the common, but not universal, practice for the chief justice to do so. While Article VI’s Oaths Clause simply requires the persons specified therein to “be bound by Oath or Affirmation, to support this Constitution,” the Presidential Oath of Office Clause requires much more than this general oath of allegiance and fidelity. The clause, in notable part, enjoins the president to swear or affirm that he “will to the best of [his] Ability, preserve, protect and defend the Constitution of the United States.”

The Framers undoubtedly drew upon similar provisions in a number of early state constitutions in drafting the clause, but they plainly believed that a special oath for the president was indispensable. At the Constitutional Convention, when George Mason and James Madison moved to add the “preserve, protect and defend” language, only James Wilson objected, on the ground that “the general provision for oaths of office, in a subsequent place, rendered the amendment unnecessary.” The prospect of George Washington’s becoming president cannot be discounted. The Framers perhaps desired an oath that would replicate the public values of the man who was presiding over the Convention. More significantly, because the presidency was unitary, there were no available internal checks, as there were in the other branches with their multiple members. A specially phrased internal check was therefore necessary, one that tied the president’s duty to “preserve, protect and defend” to his obligations to God, which is how the Founders understood what was meant by an oath or affirmation. As Justice Joseph Story noted in his A Familiar Exposition of the Constitution of the United States (1842):

A President, who shall dare to violate the obligations of his solemn oath or affirmation of office, may escape human censure, nay, may even receive applause from the giddy multitude. But he will be compelled to learn, that there is a watchful Providence, that cannot be deceived; and a righteous Being, the searcher of all hearts, who will render unto all men according to their deserts. Considerations of this sort will necessarily make a conscientious man more scrupulous in the discharge of his duty; and will even make a man of looser principles pause, when he is about to enter upon a deliberate violation of his official oath.

Presidents have traditionally sworn the oath on a Bible (Washington kissed the Bible at his inaugural) and have ended with “So help me God,” though the Constitution requires none of these gestures. A suit requesting a court order to prohibit the chief justice from prompting the “So help me God” phrase was dismissed for lack of standing. Newdow v. Roberts (2010).

The clause is tightly linked with Article II’s Take Care Clause, which requires that the President “shall take Care that the Laws be faithfully executed.” The duty faithfully to execute the laws under the Constitution might be thought to presuppose a power to interpret what is to be executed: “to say what the law is,” to borrow a famous phrase from Chief Justice John Marshall. Indeed, some scholars—and presidents—have seized upon the clause as the font of the president’s power of “executive review,” the president’s coordinate power to interpret the Constitution and what is to be “preserved, protected, and defended,” even against conflicting interpretations by the legislative or judicial departments. The penultimate draft of the clause, referred by the Framers to the Committee of Style and Arrangement and reported by that committee, provides some support for this reading. That draft provided that the president act to the best of his “judgment and power,” instead of to the best of his “ability.” However, the Ninth Circuit has declared that the Presidential Oath of Office Clause does not allow the president to suspend the operation of laws that he believes are unconstitutional. Lear Siegler, Inc. v. Lehman (1988).

Finally, the “preserve, protect and defend” language of the Presidential Oath of Office Clause might be thought to place a special constitutional duty on the president to fight for the nation’s survival, whether Congress has declared war or not. So thought President Abraham Lincoln during the Civil War.