Jesus said give to God what is God's and give to Caesar what is Caesar's. The oath is appropriate for a child of God when the oath is to support a Nation conceived under God to protect the freedom to worship and live in the presence of God.
Take the Oath
I, anon, 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.