With Plans In The Works And Troops On The Way, Military Assumes A Mostly Familiar Role On The Border

Dozens of Marines unfurled coils of concertina wire - one on the ground and one slightly above - making it more difficult to climb a border wall separating Tijuana from San Diego. They worked with speed and efficiency amid a weekend rush of cars nearby at the busiest border crossing between the U.S. and Mexico.

Fortifying barriers has long been a military task on border missions that date back to the administration of George W. Bush. But President Donald Trump has hinted strongly at the unprecedented use of the armed forces to repel what he calls a "disastrous invasion."

Until now, the military has limited itself to a supporting role at the border - surveilling for illegal crossings by ground and air, repairing vehicles, building barriers - adhering to the Posse Comitatus Act of 1878 to keep the armed forces away from civilian law enforcement.

The Associated Press toured the border in San Diego with Marines and saw a military operating similar to past missions. But some scholars and advisers close to Trump argue there are legal grounds to summon the military to combat narcotics and mass migration.

Trump's declaration of a national emergency at the southern border indicates he may redirect money, as he did during his first term, to get billions of dollars for border wall construction.