A look at George Washington and 'so help me God'

A portrait of George Washington by Charles Willson Peale. (Courtesy of Mount Vernon Ladies' Association)

A nice column by Prof. Noah Feldman; a while back I looked into this general question, and my sense is that Feldman's historical analysis is generally sound (though one can debate what relevance it should have today). An excerpt:

Did George Washington add the words "so help me God" to the constitutionally prescribed oath of office when he was sworn in as president on April 30, 1789? I've always thought so, and when discussing Kentucky clerk Kim Davis's misinterpretation of her oath of office last week, I wrote that the U.S. Constitution doesn't include the words but that Washington "famously added them." Immediately I received an e-mail citing an essay that claims this widely held view was in fact a myth, unsubstantiated by contemporary historical evidence and derived from a doubtful childhood memory by Washington Irving. I read the essay, and then found counterarguments on the web and in a good old-fashioned book.

So what's the truth? And why we should care, other than historical accuracy, which is always desirable and never perfectly attainable? I've done some research, so let me try to offer a measured answer ….