Migration between USA and Mexico used to be lower when the borders were more open. One reason was that people from Mexico were working in USA on temporary basis and emigrating from USA after some time. What Trump administration is doing is called "tough border complex". The more the border is "protected" by military, police, fence the more will individuals as from Mexico try to cross over it. Why? Well because one will try to stay in USA for as long time as possible after doing so.

The current system with federal prisons and laws on illegal migration means that US taxpayers are paying for authoritarian policies because prison companies will lobby in Washington for policies that benefit them. "Draining the sawmp", oh the irony. Aslo, the drug cartels as in Mexico are already specialized in tunnels and other means of transportation used for illegal crossings that the USA government cannot prevent.

The idea of building the wall is not only unrealistic and populist but also an idea that cannot be seen as libertarian or "secure". Because it means that US taxpayers will pay for a security theater where the government is pretending to secure and protect something. The best way to reduce illegal migration is to make migration legal. As with the case of open borders . If more people can migrate and move legally they will not have to depend on human traffickers, organized crime, potential rapists etc. Crime and other perceived problems as narcotics can be dealt with on basis of decriminalization, legalization and transnational institutions that can operate in North and South America.

https://www.econlib.org/archives/2017/10/students_for_li.html