After weeks—years, really—of debate over the Trump administration's proposed wall at the US-Mexico border, Congress will vote on a spending bill Thursday that includes $1.375 billion for 55 miles of border fence construction. In response, President Donald Trump signaled that he will declare a national emergency to get the wall built regardless. Doing so will create more problems than it solves.

Beyond the politicization of a wall as a cure-all for immigration woes, border security experts continue to stress—as they have since Trump's campaign days—that a physical wall is simply not a practical or effective way to support law enforcement at the border. While human rights and privacy groups raise important concerns about alternatives like border-surveillance technologies, or the concept of a "smart wall," the fact is that Democrats and Republicans in Congress largely agree on how to fund border patrol and enforcement technologies. And despite the pressures of a looming deadline that may yet again shut down the government, Capitol Hill has denied Trump the contiguous wall he has so adamantly championed.

"The wall is expensive and unnecessary given the current level of flow into the United States," says Alex Nowrasteh, senior immigration policy analyst at the Cato Institute. "These government mega-construction projects usually cost at least 50 percent more than what’s budgeted. We estimate that each mile of wall would cost about $36 million to construct, and it won’t have a major impact on deterrence, because most of the people coming are asking for asylum."

"It’s at the ports of entry that we can do so much more than what we’re doing." Christopher Wilson, Wilson Center

Thirty years ago, illegal border crossings at the border largely consisted of Mexican men trying to get into the US to find work. The billions of dollars the US has spent to date on physical barriers were founded in that reality. But today, despite Trump's "bad hombres" rhetoric, the majority of those approaching or attempting to cross the border are women and children seeking asylum. That often occurs at official points of entry anyway; when it doesn't, asylum seekers still generally intend to turn themselves in quickly.

Christopher Wilson, deputy director of the Mexico Institute at the Wilson Center, says that these days the most constructive funding is for "border security that isn’t about the wall."

"A lot of it needs to go to the ports of entry rather than the areas between the ports of entry," Wilson says. "It’s at the ports of entry that we can do so much more than what we’re doing, both in terms of facilitating legal travel and trade while enhancing border security."

Wilson notes that physical barriers at the border have historically been a helpful deterrent to marijuana trafficking, but that they are less effective at slowing the flow of high-potency drugs like the synthetic opioid fentanyl. These drugs can be trafficked in much smaller quantities and smuggled through legitimate points of entry like checkpoints, on airplanes, and in the mail. Cato's Nowrasteh calls the wall proposal "yesterday’s solution to yesterday’s problem—at best."

Physical barriers also don't eliminate criminal behavior; they just relocate it. "If we rely on the wall to stop individuals, and we don't also improve detection methods through technology and response through personnel, then we will find routes across the border displaced rather than deterred," says Brandon Behlendorf, a homeland security researcher at SUNY-Albany. "You also need technology—cameras, sensors, databases, et cetera—and personnel agents and support staff to secure the borders."

The widely varied geography and topography of the US-Mexico border also calls for a variety of protective measures. There's no one-wall-fits-all solution. In remote regions, where it takes time for enforcement personnel to respond to potentially illegal activity, physical barriers—like the hundreds of miles of fencing that already exists at the border—are relatively effective and help buy time for enforcement response. In areas where border personnel are based or have an established presence, such physical barriers can actually inhibit security efforts, making it logistically harder for agents to see what's going on and get to the right spots quickly.

"The border is a system constantly searching for its equilibrium." Brandon Behlendorf, SUNY-Albany

To that end, Thursday's 1,159-page spending bill earmarks three-quarters of a billion dollars for border security technology, of which $570 million must focus on "non-intrusive inspection equipment at ports of entry." Customs and Border Protection and the Department of Homeland Security have been working for years to develop an array of border-security tech tools that include body scanners, cameras, infrared sensors, and radar deployed to collectively create a sort of invisible web or dome along and across the border. Sensors are positioned on the ground, on fences, on posts, and higher up through CBP's Integrated Fixed Towers program—which is working on syncing and coordinating various types of sensors. Another crucial component is aerial monitoring from manned planes and helicopters, as well as drones and sensor-equipped blimps. Thursday's bill includes about $2.5 billion to be dispensed through 2023 on border-security-related vehicles, including drones.