The Presidential Oath of Office can be found in Article Two, Section One, Clause Eight of the U.S. Constitution. It's a brief and iconic affirmation of the duties of President, administered on Inauguration Day, usually by the Chief Justice of the Supreme Court. It goes like this:
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.
Every president in the modern era has appended the phrase--not included in the orginal text--"so help me God." The origin of the prayer is unclear. There is a report by Rufus W. Griswold In his 1854 book, The Republican Court or, American Society in the Days of Washington, Rufus W. Griswold says that George Washington said the phrase at his first inauguration.
A gesture of the Chancellor [New York] arrested the attention of the immense assembly, and he pronounced slowly and distinctly the words of the oath. The Bible was raised, and as the President bowed to kiss its sacred pages, he said audibly, "I swear," and added, with fervor, his eyes closed, that his whole soul might be absorbed in the supplication, "So help me God!"
Since it was 65 years after the event, Griswold's account is in some dispute. He never reveals the source of his description. If accurate, it reveals that Washington was not taking the oath, but affirming it, saying simply "I swear" after the Chancellor of New York spoke the words. The affirmation method of the Oath of Office is now defunct. As you can see in the video, recent presidents take the oath by repeating the words after the Chief Justice.
The oath has its share of mishaps. In 2009, Chief Justice John Roberts famously misspoke the second segment of of the oath, saying, "That I will execute the Office of President to the United States faithfully," instead of placing the word "faithfully" after the word "execute," as the Constitution prescribes. In repeating the misspoken phrase, Barack Obama paused after the word "execute," apparently realizing the mistake. To clear up any confusion, Obama retook the oath with Justice Roberts at the White House the following day.
President Obama and Justice Roberts were not first to jumble the oath. In 1909, Chief Justice Melville Fuller misquoted when giving the oath to Howard Taft, a mistake Taft later made himself when giving the oath to Herbert Hoover (Taft became Chief Justice after his presidency). In the fourth and final phrase, Taft said, "preserve, maintain, and defend," instead of "preserve, protect, and defend."
The Presidential Oath of Office has a storied history. Its next chapter will be written Monday when President Obama takes it for the...fourth time (he will have taken it on Sunday when his first term officially ran out). Check out the video above to see recent presidents on their inauguration days.