On Jan. 20, 2025, Donald Trump will take the presidential oath of office: “I do solemnly swear that I will faithfully execute the Office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States.” And then he will probably add the phrase “so help me God.”

Those four little words are not in the Constitution, but for many Americans, the phrase has been a part of the oath ever since George Washington was said to have added it 236 years ago.

But did Washington really say “so help me God?” There is no evidence that he did. In fact, no one said he did until 1854, 65 years later, when Rufus Griswold, an editor and literary critic, told the story in a book titled “The Republican Court”: “[Washington] added, with fervor, his eyes closed, that his whole soul might be absorbed in the supplication, ‘So help me God!’”

As a professor of U.S. history, I don’t care if Washington said it or not; my interest is in how quickly “so help me God” became established in the American national memory.

For a 2014 article titled “In Griswold We Trust,” I used various online databases such as Google Books, Internet Archive, American Periodicals Series and Newspapers.com to search for the phrase. Before 1854, there are........

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