Can Donald Trump really rename the Gulf of Mexico the ‘Gulf of America’ or does he need to just, like, chill?

Donald Trump’s presidency hasn’t even begun, but the president-elect is already swinging at America’s allies. A bombastic Trump is nothing new, but even after 12 years of his constant strongman impressions, the 78-year-old still manages to up the deranged — and stupid — ante.

After weeks of harassing Canada, Mexico, and Greenland over his supposed intentions to annex the various U.S.-allied countries, mind you, Trump has decided that the Gulf of Mexico should be a part of the conversation. 47 is now mulling over the possibility of renaming the body of water, but it’s going to prove more difficult than a simple assertion to change centuries of precedent.

Can Donald Trump rename the Gulf of Mexico?

The Spanish first discovered the Gulf of Mexico as far back as 1497, though it wasn’t until the 1540s that it started appearing on Spanish maps as “Golfo de Nueva España,” or “Golfo de México.” Its lengthy legacy clearly means very little to Trump, however, and his threat does have some weight behind it — though it comes with a catch.

Trump has the power to change part of the Gulf’s name, but he couldn’t rename the whole thing. The United States only owns a portion of the 930-mile-wide body of water, a claim that stretches from the southern tip of Texas to the very tip of Florida. Mexico owns the lion’s share, with Cuba possessing a sliver right down the middle. More than $2.1 billion dollars’ worth of trade moves through its waters every day, and all that dough means the other sovereign nations attached to the waterway aren’t letting it go anytime soon.

Sharing waterways is an important part of international cooperation, and while it’s not unusual for America to step on toes to get things done, Mexico and Cuba need to agree. The rules and regulations regarding America and Mexico’s treatment of the Gulf were first spelled out in the 1848 Treaty of Guadalupe Hidalgo at the end of the Mexican-American War.

Article V of the treaty laid out the boundary of the countries, leaning on the Rio Grande to act as a physical barrier. It reads,

“The boundary line between the two Republics shall commence in the Gulf of Mexico, three leagues from land, opposite the mouth of the Rio Grande, otherwise called Rio Bravo del Norte, or opposite the mouth of its deepest branch…”

The imaginary line follows the river westward to mark the boundary, which has only moved once since its inception — after the Gadsden Purchase in 1954. The treaty, which is still very much in effect today, explicitly states that,

“The boundary line established by this article shall be religiously respected by each of the two republics, and no change shall ever be made therein, except by the express and free consent of both nations, lawfully given by the General Government of each, in conformity with its own constitution.”

That’s not to say the line can’t be reworked, however. Since its inception, the boundary has been redrawn several times. Cuba reworked the line with America and Mexico in the late ‘70s after Fidel Castro was formally elected President, and in 2007 Mexico requested an extension of their continental shelf. Its request was granted, but only after extensive back and forth with the U.S. to create a bilateral agreement that both countries felt upheld their respective rights. The treaty was seen as a perfect example of cooperation for the international community.

Trump’s promises to rename the Gulf of Mexico could come to pass, but the name change would mean very little to the rest of the world. Americans would have to buy new maps — I’m sure Trump will sell some special edition versions plastered with his name — but the idea comes across as a vanity project, roughly as serious as the early 2000s cries of “freedom fries.” Treaties can take years to hammer out, even when the best negotiators are involved, and Mexico’s president, Claudia Sheinbaum, has already made it clear she isn’t looking to make friends with Trump.