The presidential Oath of Office
Article II of the Constitution, the part devoted to the executive branch, spells out the 35-word oath to be taken by the president: "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." George Washington added the words, "So help me God." It's been tradition ever since. The Constitution further declares that the president will take this oath "before he enter on the Execution of his Office."