Migration and illegal border-crossings A report in May 2008 by the
Congressional Research Service found "strong indication" that illegal border-crossers had simply found new routes.
New York Times op-ed writer
Lawrence Downes wrote in 2013: "A climber with a rope can hop it in less than half a minute. ... Smugglers with jackhammers tunnel under it. They throw drugs and rocks over it. The fence is breached not just by sunlight and shadows, but also the hooded gaze of drug-cartel lookouts, and by bullets. Border agents describe their job as an unending battle of wits, a cat-mouse game with the constant threat of violence." As of 2016, fence was routinely climbed or otherwise circumvented. The same GAO report concluded that "CBP cannot measure the contribution of fencing to border security operations along the southwest border because it has not developed metrics for this assessment." The GAO reported in 2017 that both pedestrian and vehicle barriers have been defeated by various methods, including using ramps to drive vehicles "up and over" vehicle fencing in the sector; scaling, jumping over, or breaching pedestrian fencing; burrowing or tunneling underground; and even using small aircraft. A 2019
National Bureau of Economic Research paper by Dartmouth College and Stanford University economists found that the "total impact of the border wall expansion including all
general equilibrium adjustments was to reduce the (long-run) number of Mexican workers residing in the United States by about 50,000, a decline of approximately 0.4%."
Economy A 2019 estimate by Dartmouth and Stanford economists found that Mexican workers and high-skilled U.S. workers suffered minor economic harm as a result of the fence expansion (average annual income loss of 81 cents, $1.82, and $2.73 for low-skilled Mexican workers, high-skill Mexican workers, and high-skill U.S. workers, respectively), and that on average low-skill U.S. workers benefited economically by a negligible amount (average annual income gain of 28 cents per year). The study identified the most "at risk" species as the
Arroyo toad (
Anaxyrus californicus),
California red-legged frog (
Rana draytonii),
black-spotted newt (
Notophthalmus meridionalis),
Pacific pond turtle (
Clemmys marmorata), and
jaguarundi (
Puma yagouaroundi). The study also identified coastal California, coastal Texas, and the
Madrean Sky Island Archipelago of southeastern Arizona as the three border regions where the barrier posed the greatest risk to wildlife. In Texas, for example, "the border barrier affects 60% to 70% of the habitat in the South Texas Wildlife Refuge Complex, which includes the
Laguna Atascosa,
Lower Rio Grande Valley, and
Santa Ana National Wildlife Refuges." ==Proposals for further expansion==