An atheist president would take the exact same oath, minus the words, "so help me god." Since that is an affirmation, rather than a sworn oath, there is no need for a Bible. If the president-elect was a traditionalist, he might take the oath holding a copy of the Constitution of the United States of America. read more
Presidents can take the oath of office with their hand on the bible, but this does not violate the First Amendment. Requiring them to would be a violation. As others have said, an atheist would likely use a copy of the constitution. read more
According to official records kept by the Architect of the Capitol, Teddy Roosevelt is the only president who wasn't sworn in using a Bible; he took a rushed oath of office in 1901 following the assassination of William McKinley. read more
When Bibles are used—presidents usually choose which Bible they would like to use and whether or not the Bible is open or closed while taking the oath. Many presidents choose to open the Bible and rest their hand on a specific scriptural passage and no two presidents have ever used the same passage. read more