Question? What did George Washington swear in on his oath of office on? I would think it most appropriate for all elected national leaders to swear upon the same and then take an oath to defend the constitution as written and only changed by constitutional amendment as needed. The Constitution must only be changed by Constitutional amendment and not the whims of political judges on the supreme court. If they can do this, we have no constitution.
Per the late and great scholar of constitutional law, Scalia. The only thing wrong with a living constitution is it will destroy the constitution.
The Bible which was used for swearing in President Washington, today, is housed at St. Johns Masonic Lodge in New York.