Border security is shaping up to be a major wedge issue in Washington's push to overhaul the nation's immigration laws. The unfinished Senate plan includes a so-called "trigger mechanism" that means the border has to be tightened before the nation's undocumented immigrants to have a path to citizenship. But violence and illegal border crossings are lower than they've been in decades. Molly Ball has been looking into the state of our borders for The Atlantic magazine. She joins the show from Washington.