It's nice that the President is letting Justice Roberts do the oath in private

in case Roberts screws up again

In 2009, Chief Justice John G. Roberts, while administering the oath to Barack Obama, incorrectly recited part of the oath. Roberts prompted, "That I will execute the Office of President to the United States faithfully." Obama stopped at "execute," and waited for Roberts to correct himself. Roberts, after a false start, then followed Obama's "execute" with "faithfully", which results in "execute faithfully," which is also incorrect. Obama then repeated Roberts' initial, incorrect prompt, with the word "faithfully" after "United States."[16][17] The oath was re-administered the next day by Roberts at the White House


The oath of office of the President of the United States is an oath or affirmation required by the United States Constitution before the President begins the execution of the office. The wording is specified in Article Two, Section One, Clause Eight:


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."

"So help me God"
http://en.wikipedia.org/wiki/Oath_of_office_of_the_President_of_the_United_States