US Customs

U.S. Customs and Border Protection is testing mobile surveillance towers like this one, parked at the Border Security Expo in San Antonio, to improve the tracking of illegal crossers. Critics of the border wall say the government should favor virtual technology over steel and concrete. John Burnett/NPR hide caption

U.S. Border Patrol next to the the border wall dividing Nogales, Ariz., and Nogales Mexico. Susan Schulman/Barcroft Media via Getty Images hide caption