What force is driving the surge in migrants at the U.S. border?

As the Senate appears ready to rebuke the president’s national emergency declaration, border officials are warning that the flow of people arriving at the Southern border is pushing the system to a “breaking point.” Ali Velshi and Stephanie Ruhle are joined by NBC’s Julia Ainsley to discuss this record surge, what the scale actually is, and what’s driving it.March 6, 2019