Deport them on the spot is allowed.
Deport them and they will drift down a hundred miles and cross somewhere else...don’t wait til they are at the border. Trump should tell the Mexican President he will not allow any truck or rail car to enter the US until it has been searched from top to bottom for drugs...a process that would take months...meaning the hundreds of millions of dollars in Mexican produce will rot...unless the Mexican Pres. sends these invaders back to their home country.
If Trump allows them entry he will be finished politically, his popularity will drop. He will have Merkalized himself. Act now.