A report by the AP reveals:
This could, under certain circumstances, mean directing troops to temporarily detain migrants in the event of disorder or violence against border patrol agents. “This is minutes — not even hours” of potential detention, Mattis said, suggesting that he was not planning to use the military to operate migrant detention camps.
“We’ll keep you posted on any new missions and any new numbers of troops as those decisions are made,” he said.
The mission thus far for the approximately 5,800 active-duty troops in the border area has been mainly to lay barbed wire and other barriers along the border and to transport border patrol personnel. Mattis has stressed the need to keep the military away from civilian law enforcement roles such as arrests, which are forbidden under the Posse Comitatus Act. The law prohibits the federal government from using the armed forces in a domestic police role, except in cases and under circumstances specifically authorized by the Constitution or Congress.
The basis for the expanded legal authorities for Mattis is a belief by the Trump administration that the caravans of Central American migrants, whose numbers include many families with children, moving toward the U.S. border pose a potential security threat to the border patrol.