The oath of office of the President of the United States is an oath or affirmation required by the United States Constitution before the President begins the execution of the office. The wording is specified in Article Two, Section One, Clause Eight:
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.
Let's face it, folks. He LIED.