I swear it's true

The Presidential oath of office is described in Article II, section 1 of the Constitution:
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."

Nothing in this section requires that the oath of office be taken on the Bible. Neither do the words "so help me God" appear in the oath. While Presidents often include this phrase in their inauguration ceremonies, the words are customary; they are not required by the Constitution and have no legal significance.

God help him who doesn't swear unto God!