181121-M-SK635-281 SAN LUIS, Ariz. (Nov. 21, 2018) Marines assigned to 1st Combat Engineer Battalion, Special Purpose Marine Air-Ground Task Force 7, fortify the Arizona-Mexico border with concertina wire near the San Luis Port of Entry in Arizona, Nov. 20, 2018. U.S. Northern Command is providing military support to the Department of Homeland Security and U.S. Customs and Border Protection to secure the southern border of the United States. (U.S. Marine Corps photo by Cpl. Cutler Brice/Released)