It is likely that most readers have watched an incoming president recite the oath of office. That oath is prescribed in Article II, Section 1 of the U.S. Constitution:
I do solemnly swear (or affirm) 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.
Somewhat surprisingly, the Constitution does not specify an analogous oath for other officeholders. Article VI, however, states that there must be such an oath (or oaths):
The Senators and Representatives before mentioned, and the Members of the several State Legislatures, and all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution; but no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States.
Beginning in 1789, Congress employed a succinct oath:
I do solemnly swear (or affirm) that I will support the Constitution of the United States.
The outbreak of the Civil War led to an expanded congressional oath, an oath that has been modified several times since then. Senators now take the following oath:
I do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter: So help me God.
The enhanced oath seems especially pertinent in 2022.
Members of the House of Representatives take the same oath, though the name of the representative is inserted after the initial “I.”
Traditionally, incoming presidents append “So help me God” to their oath. Given that the Constitution was intended to create a secular government—the word “God” does not appear in the document—both this addition and the corresponding official endings of the congressional affirmations are contrary to the spirit of the Constitution.
Perhaps someday, an incoming atheist legislator will object to his or her oath of office as unconstitutional. Likely, however, courts will argue that “So help me God” does not constitute a religious test for office. Instead, they will dismiss it as an instance of “ceremonial deism,” a rationale used to justify the use of “In God we trust.”
NOTE: I am not a fan of ceremonial deism. See my essay “A Matter of Mottos.”