WATERMARK

The oath or affirmation of office of the President of the United States was established in the United States Constitution and is mandatory for a President upon beginning a term of office. The wording is prescribed by the Constitution (Article II, Section 1, Clause 8), as follows:

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.

Please note — preserve, protect and defend the Constitution —

Not the people, not the party, not the boundaries nor the ideologies of any particular religion or philosophy.

The Constitution.

ADDED, thanks to Anne:

Things That Are Not In the U.S. Constitution