You cannot renounce US citizenship while in the US. You can only do it in person at a US embassy or consulate, and you often have to make at least two appearance there over at least two months.
In the movie French Kiss, Meg Ryan renounced her American citizenship without first acquiring Canadian citizenship.
Oops.
What if he tells State he’s a citizen of the World? He can prove it by singing the global anthem.
https://www.youtube.com/watch?v=ne7fPpxAnuM