In this Tuesday, Sept. 15, 2015, photo U.S. Customs and Border Patrol agents patrol along the border fence in Hidalgo, Texas. The staggered fence or “wall,” costing $6.5 million per mile, runs along 54 miles of Texas’ 1,254-mile border with Mexico. Adding to the Texas wall may be difficult, courtesy of the border’s sheer length, the fact that it sits in the center of the snaking Rio Grande, and because international treaties with Mexico prevent either country from constructing within the river’s flood plains. Finishing the some 1,300 miles of border fencing would also be expensive, costing billions of dollars to complete. (AP Photo/Eric Gay)