Oath of office of the President of the United States
The oath is ordered by the United States Constitution (Article II, Section One, Clause 8), and is given before the President begins his term of office.
This is what the oath says:
“I (name of president) 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.”
- "United States Code: Title 28,453. Oaths of justices and judges | LII / Legal Information Institute". Law.cornell.edu. 2010-01-21. Retrieved 2010-08-07.