He may have "renamed" the Gulf" however there is an internationally accepted protocol for naming seas and oceans, not that Trump cares about protocols too may syllables for him.
IHO (International Hydrographic Organization): The IHO, in collaboration with the IOC (Intergovernmental Oceanographic Commission), plays a key role in standardizing undersea feature name
Three countries have an interest in the Gulf of Mexico, not just USA, they have a say, another ego/vanity crapola from Trump