Obama is a Christian.President Obama will end the oath with
"so help me God" illustrating the influence of Christianity on America in 2013
In the USA, we have that choice... religion.
It's not like in the UK where politicians have to swear allegiance to the head of the Church of England.
If Obama felt like it, he could have said so help me "Great Flying Spaghetti Monster".
He- like all Americans- has that choice.