Every public servant, such as a judge, Senator, or Congressman, makes a personal oath when entering into such a position. It is required by the Constitution.
The Presidential Oath is set forth in the Constitution as: “I do solemnly swear 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.”
When being sworn in as our first President, George Washington spontaneously added the words: “so help me God.” This has becoome a traditional part of the Oath of office.