I'd just like to add that in the UK Parliament, the boxes which you might see the Prime Minister rest his documents on.....is full of bibles.
The unspoken assumption is 'swearing on the bible'. or 'all words spoken here are in truth'....well.....who knows
I'm for the Green Eggs 'n' Ham option. It would be more honest, perhaps.
The point I'm trying to make is that it is rather irrelevant. He will do as well as he will do. What he is sworn in on is no longer particularly relevent to his real consciousness within the world.