Since he started his campaign last year President Trump has promised to build a "big, beautiful wall" along the southern border of the United States.
While there's been a lot of discussion about illegal migration and whether or not the wall can help stop it, everyone has overlooked one group that crosses the border whenever they feel like it: animals.
According to the US Fish and Wildlife Service, there are 111 animal species and 108 types of birds that would be impacted by a border wall, and experts agree that the change would be very bad for the animals.
If the finished wall lives up to Trump's promises, it will be nearly 2,000 miles long and be anywhere from 30-50 feet high. Originally it was meant to be made out of concrete, but new plans might just involve a tall fence. Either way, the wall will cut lots of animal's habitats in half and have a huge impact on the environment.
Animals cross back and forth from Mexico to America for lots of reasons. To migrate when the seasons change, to look for safer habitats or to follow their food source. A wall would trap animals on both sides, but also make life harder for them.
If small animals and plants (like native cactuses and flowers) start to die out because the wall cuts them off from the best habitats, eventually the larger animals that depend on them will suffer too.
Even animals that can fly over the wall will be affected. More than 100 bird species - including the bald eagle - live near the border. While they could cross from one side to the other, they eat plants and animals that would be separated by the wall.
Tim Keitt, a biology professor from the University of Texas, compared how the wall would affect animals to building a second Grand Canyon.
He says that in the past few years, animals that had their numbers almost wiped out in America - like jaguars, ocelots and Mexican wolves - were slowly moving back into the South by crossing the border.
If the wall is built America may end up saying goodbye to those species forever.