This is what I found.
The Constitution does not provide the wording for this oath, leaving that to the determination of Congress. From 1789 until 1861, this oath was, "I do solemnly swear (or affirm) that I will support the Constitution of the United States." During the 1860s, this oath was altered several times before Congress settled on the text used today, which is set out at 5 U. S. C. § 3331. This oath is now taken by all federal employees, other than the President:
"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."
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