How “So help me God” Is Becoming Constitutional

It is by subscribing to the inaugural oath, as set out in the Constitution, that the US president elect becomes the US president. It reads: "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." Article II, Sec. 1.