The oath of office of the president of the United States is the oath or affirmation that the president of the United States takes upon assuming office. The wording of the oath is specified in Article II, Section One, Clause 8, of the United States Constitution, and a new president is required to take it before exercising or carrying out any official powers or duties.

Before he 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.”

https://en.wikipedia.org/wiki/Oath_of_office_of_the_president_of_the_United_States