1. There already is a "wall" along about a third of the border
The border runs about 1,900 miles from the Pacific Ocean to the Gulf of Mexico. Some sort of barrier—made from concrete, steel mesh and/or barbed wire —currently stands along about a third of it, in areas U.S. Customs and Border Protection deems vulnerable to illicit cross-border activity. Some segments are a solid metal wall; others are composed of various materials and have spaces between barriers or mesh, making those sections less a wall than a fence.