These are the border officers that migrants fear – and they are not the Americans

The rust-colored barrier soars into the cloudless blue sky, a solid and almost impassable marker of the border between Mexico and the United States. But then it stops, when the rough, hilly terrain becomes a mountain, or a large boulder blocks the way.

These are the spots well known by human smugglers, who bring migrants in vans, show them the gaps, tell them to head north and to call 911 if they can’t find US Border Patrol officers to hand themselves in.

A few months ago, sometimes hundreds of people...