People who live and work along the southern border of the U.S. will tell you that the farther away the political debate occurs from the border, the more detached it becomes from the reality of life in the borderlands. That long-held view has been confirmed yet again as the wrangling in Washington over President Donald Trump’s demand for $5.7 billion to build a wall along the border devolves into an argument over whether such a wall should be concrete slab or steel slats.

The reason to build a wall is to keep people out. Yet history is replete with examples of walls all over the globe that rarely deterred determined people from getting in. Janet Napolitano, who served as governor