David V. Aguilar is taking retirement and will step down as the head of U.S. Customs and Border Protection, the Department of Homeland Security announced late Friday. In an e-mail to employees, Aguilar said his retirement takes effect at the end of March. Aguilar has led the border management agency for more than a year over two stints. Aguilar rose through the ranks and became chief of the Border Patrol in 2004 in the early days of its integration with U.S. Cust...