Bringing us back to the contemporary, what would “success” for the US Southern Border Wall be?
The first thing that has to be accepted is that the scale of illegal immigration from Mexico is staggering with huge effects on the United States.
Likewise, according to the same Pew Research centered, illegal immigrants currently account for some 3.5% of the US population. With regard to Mexican immigration, this is most readily felt in parts of the country where few people go, the small towns. There is a map created which represents every person on the US census as a color-coded dot –
Zooming out shows the map as apparently completely blue, but when you zoom into many areas, such as my town highlighted with the arrow above and shown below, you see the homogenous blue zones suddenly become remarkably racially diverse.
Why my town, as well as so many towns, become suddenly homogeneously blue as you zoom out, I don’t understand, but I do understand that this is a mostly invisible issue to many who do not live in small towns like mine, nor are the externalities of it. Those externalities include that the low wage low skill jobs that employed the majority of the population are gone. There are still people doing them, but much of the work for people starting their careers have shifted to immigrant and often illegal labor. Secondly, is the impact on the schools. In my town, the population has shifted from 5% Mexican population in the 1970’s, to around 50% today. In general, this isn’t a problem except when we factor in for illegal immigrants. I’ve polled Mexican-American students at the school who volunteer that they believe at least 25% of the students are living in the United States illegally. By that, we can estimate that some 8 to 10% of the students of the school are not legally supposed to live in the town or the country for that matter. These students do have access to the same education and the same resources but are not bearing the same tax burden. For small towns like mine, having 10% of the students not contributing to the tax base is devastating to the educational standard provided, with ripple effects that can be felt for generations. This, along with many other factors, is part of why Oklahoma education is facing an existential crisis.
Likewise, let’s look at some numbers from the US Federal Sentencing Commission in 2015. Illegal immigrants accounted for 37% of all federal crimes, discounting all immigration-related federal crimes, this accounts for 14% of all federal crimes. In that remaining category, they accounted for 75% of drug possession, 30% of kidnappings, 21% of national defense crimes such as exporting arms, munitions or military equipment, and providing material support to foreign terrorist organizations, 18% of drug trafficking, 10% of money laundering, and 5% of all murders. 
I want to be clear, this isn’t saying that Mexicans are bad people or even that all illegal immigrants are bad. I don’t even believe the majority are guilty anything more than knowingly attempting to subvert our immigration laws, but all of these crimes… should not be able to happen at all. We simply must accept that the United States would be better off with fewer people selling drugs, fewer kidnappings, and fewer murders, and if an easy to prevent much of that is tougher enforcement of immigration law, then great.
Similarly, the economic burden placed on our rural labor force and education systems should not be happening at all.
That is how we will be able to measure if the Southern Wall will be a success. If it can dramatically reduce the influx of illegal immigration as well as the crime coming through or dependent upon an open Southern border, then it will be a success.
Having established that, let’s ask first if there is evidence to support the building. San Diego built their own wall and saw perhaps the best proof we need.
The wall in San Diego reduced illegal immigration apprehensions by 95%.
Back then, Border Patrol agent Jim Henry says he was overwhelmed by the stream of immigrants who crossed into the United States illegally just in that sector.
“It was an area that was out of control,” Henry says. “There were over 100,000 aliens crossing through this area a year.”
Today, Henry is assistant chief of the Border Patrol’s San Diego sector. He says apprehensions here are down 95 percent, from 100,000 a year to 5,000 a year, largely because the single strand of cable marking the border was replaced by double — and in some places, triple — fencing.
Furthermore, let’s look at the national level implementation in the US. Most illegal immigrants to the US actually came over in the 1990s when apprehensions reached a staggering 1.6 million per year.
Policies beginning around the time of 2000 halted much of the illegal immigration into the US but just as much was the 2006 Secure Fence Act, which saw the construction of 653 miles of reinforced fencing along the U.S.-Mexico border. Due mostly to this, US Border Patrol now is forced to make far fewer apprehensions. Extending the 653 miles would further reduce the need for US Border Patrol agents to make what still amounts to a quarter million apprehensions a year.