September 17, 1787.

On September 17, 1787, members of the Constitutional Convention signed the final draft of the Constitution.

Before [the President] enter on the execution of his office, he shall take the following oath or affirmation: "I do solemnly swear (or affirm) that I will faithfully execute the office of President of the United States, and will, to the best of my ability, preserve, protect, and defend the constitution of the United States."