Marchers in El Paso protest President Trump’s proposed border wall on Jan. 26. (Jose Luis Gonzalez/Reuters)

IN THE eight-year period ending in 2015, the federal government spent $2.3 billion building an array of fencing, some formidable, some flimsy, along more than 500 miles of the southwestern border. Yet when the Government Accountability Office issued a comprehensive report last year on border security, it noted that Customs and Border Protection could not assess the efficacy of those barriers, having developed no metrics to do so.

No wonder that when CBP Commissioner Kevin McAleenan submitted 18 pages of written testimony to Congress on border security last spring, he devoted just a few paragraphs to what he called “physical barriers.” He said they had “enhanced” the agency’s overall capability in securing the border, but offered no evidence.

That is the trouble with President Trump’s insistence that spending $5.7 billion on more than 200 miles of additional, more-imposing barriers — his “beautiful” wall — would defeat illegal border crossers, drive down crime and impede drug trafficking. It’s not that a huge new border wall is immoral, as Speaker Nancy Pelosi (D-Calif.) contends. It’s that barriers are just one element in impeding the cross-border flow of undocumented migrants, drugs and crime, and probably not the most effective one — let alone the most sensible use of $5.7 billion. What’s more, other steps to fortify the border could be taken more quickly and have a bigger impact.

Building hundreds of miles of walls would take years given the likely legal challenges by private landowners who own most of the border-facing property that doesn’t already have fencing, especially in Texas. By contrast, a surge in hiring additional Border Patrol agents could deliver more bang for the security buck. The agency, which is chronically understaffed, is notorious for an attrition rate that outstrips a hiring process that often takes about a year. In May 2017, the agency’s personnel on the southwestern border was roughly 1,450 officers shy of its authorized manpower of nearly 18,000.

Why not use a chunk of that $5.7 billion instead to achieve better pay and perks and streamlined hiring procedures to improve the Border Patrol’s ability to recruit and retain competent applicants who might otherwise balk at a career that can include stints in remote areas?

The existing border fencing, 654 miles of it, is generally in places that make sense as a deterrent to illegal crossings in high-traffic areas. Often, however, it is notably permeable; Customs and Border Protection recorded about 9,300 breaches between fiscal years 2010 and 2015 — roughly three or four daily — with repair costs averaging nearly $800 per breach.

That is one reason the agency has for years put a premium on electronic and other means of surveillance along the border — the “smart wall” that features cameras, sensors, drones and, at legal ports of entry, where most illicit narcotics cross the border, advanced X-ray technology that can detect contraband hidden inside trucks and smaller vehicles. As Homeland Security analysts noted in a 2017 report, the key to achieving “operation control” along the border, whereby authorities are aware of most illegal activity at the frontier, is a combination of what security experts call “domain awareness” and intelligence — not a barrier the height of a three-story house.