Following President Trump orders U.S. marines arrived at the Southern border

500 sailors and Camp Pendleton Marines join about 2,500 troops already deployed to the border to assist U.S. Customs and Border Protection.
Active duty troops are barred by law from conducting law enforcement within the U.S., which limits them to a supporting role.
The border mission is led by U.S. Northern Command, which is responsible for military operations in the continental U.S.