The best that historians can say is that the oath has ended with "so help me God" at least since Chester Arthur's inauguration in 1881.

VOA: special.2009.01.19

You ask what I am thinking. So help me, God, an immortality of fame.

你问我在想什么，愿上帝帮助我，我想永垂史册。

耶鲁公开课 - 弥尔顿课程节选

So help me God. So help me God. Congratulations.

VOA: special.2009.01.19

The ceremony was held under the pine trees with Stumpy saying the simple works: "I proclaim you Thomas Luck, according to the laws of the United States and the state of California, so help me God."

VOA: special.2009.06.06