...the fact of the matter is, if it's someone who says that the Koran is going to... supersede the Constitution, then I think most Americans are gonna say, “You know what, we've got a problem with that” – 'cause we put our hand on the Bible and we make a pledge to uphold the laws and the Constitution of the United States.
Yes, he actually appealed to the centrality of the Bible in explaining what would be wrong with putting the Koran ahead of the Constitution. And yes, he seems to be completely oblivious to any problems associated with that. What's more, this sort of thing is actually quite common among conservative Christians, as can be seen by the widespread support (including from presidential candidate Mike Huckabee) for Kim Davis, the Kentucky county clerk who violated the Constitution “on God's authority.”
Of course it would be a problem to have a president who says the Koran legally supersedes the Constitution. And for exactly the same reason, it would be a problem to have a president – or a county clerk – who says such a thing about the Bible.