David B. Parker is a professor of history at Kennesaw State University who specializes in Civil War history. As any academic historian steeped in the Civil War knows, there are sometimes two conflicting histories, the history found in the historical record and a popular "history" that originates in someone's head the same way as fiction originates, but is nevertheless promoted as factual by individuals or groups with political, commercial, or other such non-academic agendas, and is subsequently repeated over and over again by growing numbers of other people, and as a result becomes accepted by public opinion as being factually true. This happens in multiple different contexts. If you think that Abraham, Moses, and Jesus are likely fictional characters (unlike the historical warrior Abū al-Qāsim Muḥammad ibn ʿAbd Allāh ibnʿAbd al-Muṭṭalib ibn Hāshim (a.k.a. Muhammad) or the historical con-man Joseph Smith) you may want to keep this insight to yourself lest you be mischaracterized as a foolish atheist ideologue who disregards the generally accepted evidence that all sensible people, including non-religious people and people of other religions, allegedly know demonstrates that these were historical people.
And so it is also with the claims that George Washington appended "so help me god" to his first presidential oath of office and all subsequent presidents did the same. For many years the Senate Historical Office, speaking as the experts on presidential oath history on behalf of the U.S. Senate, and therefore also on behalf of the United States government, endorsed the first claim as historical fact. For multiple years, starting shortly after we began our correspondence with them, they also published a "so help me God" video on the Joint Congressional Committee for Inaugural Ceremonies' (JCCIC) website that endorsed the second claim as historical fact. Years after several of us first corresponded with the Senate Historical Office to point out that neither claim is supported by the historical record, they continued to endorse both "facts" on the website. The Senate Historical Office justified their stance by pointing out that historian Douglas Southall Freeman, who won a (posthumous) Pulitzer Prize for his six-volume biography of Washington published in 1954, claimed GW appended that phrase. We responded that the eyewitness document cited by Freeman in his biography did not assert that GW appended that phrase. From then on we got no more responses from the Senate Historical Office to any correspondence we sent them. Even though they eventually conceded their second claim was not justified they continued to assert it on the website. Frustrated by the years of no response from the Senate Historical Office, one day I visited the Senate Rules Committee office, which owns the JCCIC web site. I was dismissed by the youthful staff there, somewhat rudely, as if I was a crank.
Yet people did pay attention and began reporting the history correctly, and the JCCIC website eventually also followed. Professor Parker subsequently took an interest in the origin of these two related myths about George Washington's first inauguration and about all presidential oaths. His conclusions were recently published in Common-place The Interactive Journal of Early American Life, volume 15, no. 1 and are available for all to read under the appropriate title "In Griswold We Trust".