The US hasn't switched to calling the Gulf of Mexico the Gulf of America. Partisans on the right do this to show their allegiance to Trump. Partisans on the left still call it the Gulf of Mexico to show their opposition to Trump. Big companies that can be targeted by Trump call it the Gulf of America to protect themselves. And most non-partisans still call it the Gulf of Mexico because they're not paying attention and have always called it that (if they have ever spoken of it or know that it exists). I suspect a lot of people call it the Gulf, already an established custom before this idiocy about renaming it, precisely to avoid entangling themselves in the partisan fight.

The US, like other countries, doesn't get redefined with every change of government, and Trump has not yet cowed the public into knuckling under to his every dictat.