Every year, nearly a half million people cross the U.S.-Mexico border illegally. Most end up in California, Texas and Arizona. The Southwestern states want Congress to control the border. To make a statement, some volunteer vigilante patrols, known as the Minutemen, recently staked out a stretch in Arizona. For a while, crossings virtually stopped. But in the second part of Marketplace's series, Undocumented War, reporter Scott Carrier finds the flow of immigrants sometimes shifts, but it doesn't stop.