"It's peaceful now," the retired agent says as he stands in front of the enormous wall that separates the United States from Mexico, near the town of San Luis, Arizona.
On the eve of the midterm elections, this arid region in the Southwest serves as proof that Donald Trump kept his central campaign promise: to restore order at the border.
In the sector around San Luis, the Border Patrol now apprehends fewer than 10 people per day -- a sharp decl…