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.
You may have noticed that Supreme Court Chief Justice John Roberts said “So help me God” at the end (and Obama repeated after him). But that’s not part of the official of the oath, is it?
No, and in 2008, Michael Newdow filed a lawsuit (PDF) to prevent exactly this scenario from taking place:
Defendant Roberts… will (with no authority whatsoever) alter the text of that document to infuse the inaugural ceremony with purely religious dogma.
Newdow also laid out the history of those four little words. Basically, no president said the words “So help me God” until “1881, ninety-two years after George Washington’s initial ceremony” — when “Chester A. Arthur took the oath upon hearing of President James Garfield’s death.” After that it didn’t become a “tradition” as we know it until 1933 (with Franklin Roosevelt). In short, there was no reason to continue this “tradition.”