Quote from : Understanding Power: The Indispensable Chomsky Book

Actually, Bush, technically speaking, is not really President-because he refused to take the Oath of Office. I don’t know how many of you noticed this, but the wording of the Oath of Office is written in the Constitution, so you can’t fool around with it-and Bush refused to read it. The Oath of Of­fice says something about, ”I promise to do this, that, and the other thing,” and Bush added the words, ”so help me God.” Well, that’s illegal: he’s not President, if anybody cares.