Some of it comes through tunnels, ships, trucks or planes, but a lot comes across border in drug mule backpacks. The term "wall" is symbolic, referring to all of the measures that could be used to stop the invasion of the US by drug cartels, illegals, criminals and terrorists. The US hasn't even bothered to officially deport people to make it a crime to come back. There's so much drug cartel money floating around, it's just too tempting for some people to ignore the problem.