You'll lose everything you may have as a US citizen.
No, you do not have to give up dual citizenship in order to join the military.
Anyone who is a citizen of the Vatican maintains their original citizenship of their country of origin. Should they lose their Vatican citizenship they revert to their original nationality or, lacking that, automatically become Italian citizens.
No - citizenship is not transferable from one person to another !
You never lose US citizenship unless you either renounce it voluntarily or by serving in the army of a country that is in war with the US.
If you "renunciate" something, you give it up.
to lose or give up
Apply at the nearest embassy or consulate of your country of citizenship.*Your case would not be approved usually if you do not have another citizenship.
expatriation
Look - up U.S. Immigration & Citizenship Your Complete Guide
No, a former president cannot give up their citizenship. Once someone is a citizen of a country, they retain that citizenship unless they voluntarily renounce it through a formal process. Being a former president does not exempt someone from the normal rules and procedures regarding citizenship.
give up your Indian citizenship
Mark Zuckerberg did not renounce his US citizenship. He did, however, give up his US citizenship while acquiring citizenship in other countries to avoid double taxation on his assets.