Be gratious and move on. Part of being in the public eye is that you're going to flub some days. This was a historic day and a world event so there's no where to hide on this one. If I were President Obama and Chief Justice John Roberts I would do exactly what they are doing - taking this as an opportunity to role model how to not let a mistake get in the way of getting down to business and moving on with the work that needs doing. People make way too much over public humiliation. If you are going to do anything in this world, it's going to happen to you too. The world didn't end. The oath has been re-taken. The great oratory of the day and the flub of the day should in combination inspire all of us to take a second look at all those great opportunities out there to prepare ourself for the 2 minutes of glory and the 2 minutes of shame that will come our way. Think of all the offers you've received and give a second look at an opportunity to build your confidence and self-assurance in speaking in high pressure situations.