And, where can the actual oath be found? It is at the end of Article II, Section 1. You can find it here on the Cornell LII site. Section 1 reads -
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."A careful review of one YouTube video of the many posted will show you that it was Chief Justice Roberts, not President Obama, that made the mistake.