The town of Arivaca, Ariz., is 11 miles from the border with Mexico. It has become a magnet for self-styled militia groups from out of state that say they want to patrol the border and stop migrants.

The town of Arivaca, Ariz., is 11 miles from the border with Mexico. It has become a magnet for self-styled militia groups from out of state that say they want to patrol the border and stop migrants.