The new wall not only lowers apprehensions but allows the border officials to make the arrests closer to the border and not in border communities.
In November last year, a caravan of hundreds of migrants approached the U.S.-Mexico border near San Diego and faced old landing-mat border barriers erected decades ago. Border agents say the migrants simply trampled over it as they sought entry into the United States to claim asylum as part of migrant waves that would overwhelm authorities.
How effective it is being in terms of both deterring migrants and stopping crossings is tough to calculate. One thing that is clear is that the erection of the barrier is coinciding with a sharp decline in apprehensions, although correlation does not necessarily equate to causation. In August, there were 3,326 apprehensions in the San Diego sector, down from 6,880 in March and 5,884 in May.
That reflects a border-wide trend that has seen apprehensions along the border as a whole drop almost 65 percent since May, as part of a multi-faceted strategy from the administration that has included not only barrier construction, but also agreements such as the Migrant Protection Protocols (MPP) -- by which tens of thousands of migrants have been returned to Mexico while they await their immigration hearings.
Harrison said that while the wall makes a significant difference, it is hard to state categorically how much of the decline can be attributed to the wall alone.