https://en.m.wikipedia.org/wiki/Oath_of_office_of_the_President_of_the_United_States
"The oath of office of the President of the United States is the oath or affirmation that the President of the United States takes after assuming the presidency but before carrying out any duties of the office. The wording of the oath is specified in Article II, Section One, Clause 8, of the United States Constitution.
This clause is one of two oath or affirmation clauses, but it alone actually specifies the words that must be spoken. The other, Article VI, Clause 3, simply requires the persons specified therein to "be bound by oath or affirmation, to support this Constitution." The presidential oath, on the other hand, requires much more than this general oath of allegiance and fidelity. This clause enjoins the new president to swear or affirm that he "will to the best of his ability, preserve, protect and defend the Constitution of the United States."[1]
Text
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."[2]".....(more)