The Atlanta Journal Constitution reports here that Mexico just sends their problem north to us, and Bush's law requires us to waste time and resources tracking down the traffickers, all while it's in Obama's political interests to be lenient:
Fleeing punishing poverty and brutal gangs, tens of thousands of people from El Salvador, Guatemala and Honduras started surging across the border in 2014. Their numbers fell toward the end of that year and stayed lower in early 2015 before rising sharply again. Between October of 2015 and January of this year, apprehensions on the southwest border were more than double the number from the same period the year before. Most of those who were caught are from Central America. Some are from Mexico. ...
A 2008 anti-human trafficking law — signed by President George W. Bush — prevents the government from immediately deporting them. Instead, the government is required to feed, shelter and provide medical care to them until they can be released to the care of sponsors, who are usually relatives. Meanwhile, the children undergo deportation proceedings in federal immigration courts in Georgia and other states where they can seek relief to stay in the U.S. ...
[T]he government is in a better position to respond to the surges this year because it has opened several processing centers — converted warehouses — for the apprehended immigrants in McAllen, Texas. At those centers, authorities try to identify their smugglers and the routes they took to get into the U.S.
One impediment to building a decent wall to stop this flood is that much of the border land is privately owned.
Now you understand why Trump is talking up eminent domain. Talking about taking land to build a pipeline from Canada to the Gulf is simply preparation for taking land to build the Great Wall of Trump.