During his first week in office, President Donald Trump signed an executive order to fulfill one of his campaign promises -- to build a steep wall along the 2,000-mile U.S.-Mexico border. Saying the U.S. government has failed to secure its southwestern border, a group of armed citizens patrols a nearly 400-mile stretch of desert land that separates Arizona from Mexico. The group, Arizona Border Recon, describes itself as a surveillance organization ready to interdict illegal immigrants and illicit drugs entering into the country. But state and federal law enforcement agencies see the group as getting in their way. On Saturday, NewsHour Special Correspondent Nick Schifrin introduces us to the group and its detractors.