Swearing in American presidents on the Constitution, not the bible

As Barack Obama gets ready to take office, a thought has been plaguing me. Why are our presidents and for that matter all of our elected officials sworn in on the Bible? We are not a Theocracy, we are a Democracy, and the guiding tenets and principals of that Democracy are not laid out in the Bible, but in the constitution of the United States of America. In fact, if we adhere literally to the bible we would not have much of a democracy at all. We'd have a nation which sacrifices it's sons, turns people to stone, and accomplishes most things with some sort of violence. And there's the point. Besides the turning to stone part, we as a nation HAVE sometimes adhered to the laws of the Bible, more often than not at the peril of the laws of our nation. We are not answerable to a higher power as Americans. We are answerable to our constitution and our own moral compasses. I am calling for a changing of the guard. if Mr Obama truly wants to swear his allegiance to a worthy American document which protects all of us, not just the religiously faithful, he and every public office holder after him should have their hands squarely placed on the original copy of the constitution of the United States.