Another important bit of context, (supplied by NY Times, Nov., 2015): 2015 was the year the US recorded that there were more Mexicans LEAVING than US than entering the country--legally or illegally.  Over a period of a few years, the "leaving" tally was 140,000 over the "arriving" tally.  

Now, many would jump to the conclusion that, "Aha!  See?  life in the US wasn't so good after all!"  Well, that may have been the case for some, but the more important reason that out-migration was bigger than in-migration was...beefed up border patrols by legitimate US services and vigilante groups. It was simply tougher to get in.  

And--wow--all this long before the Presidential election!  Why spend a ton of money building a "wall"?  Could it be...politics?  Just like "top of the pack" military build-up.  Pointless, when you already have close to 7,000 nukes at your disposal.  Smacks of JFK's "Missile Gap" (1958)  Pure politics, and even Saint Kennedy wasn't above doing it to win an election.