So here are some simple graphs that tell the real story.
1. Net migration between Mexico and the US is zero.
For a quick summary of why this is changing, here's Simon Rosenbberg.
Contrary to what the nativists would have us believe, we are not being overrun by hordes of Mexicans coming here illegally. What we have is a group of approximately 11 million undocumented people - most of whom have been living here in the shadows for quite a while. It is in everyone's best interests to give them a path to citizenship.
And if we want to stem the current flow of immigrants from Mexico, we might think about ending the reason many of them continue to flee their homes...the violence associated with the war on drugs.