Expanding the wall and fencing along the border and adding military personnel to patrols there are unlikely to interrupt the most common smuggling method.
Reinforcing the southern US border has been a high priority for President Donald Trump, who has promised since the early days of his campaign to construct additional barriers along the frontier.
This month, in an apparent response to an annual migrant caravan heading north through Mexico toward the US border, Trump announced that he would deploy the National Guard for additional security at the frontier — against both the unauthorized movement of people and the illicit transport of illegal drugs into the US.
"We're putting the National Guard and military at the border," Trump told reporters on Monday. "And we need a wall. Whether you're a Republican or Democrat, we need a wall, and it'll stop your drug flow. It'll knock the hell out of the drug flow, and it'll stop a lot of people that we don't want in this country from coming into our country."
US military personnel at the border will be authorized only to assist the Border Patrol with intelligence and surveillance and won't have the power to capture migrants. But it's questionable how much more additional enforcement they could provide.
The 2,000 to 4,000 troops Trump wants to deploy will arrive at a time when there are 30,012 border apprehensions a month, according to the Washington Office on Latin America. When President George W. Bush deployed the National Guard to the border in 2006, there were 128,979 apprehensions at the border a month.
And based on reports from the US Drug Enforcement Administration and other government officials, more troops along the border may miss the mark when it comes to staunching the flow of illicit narcotics into the US.
The US Drug Enforcement Administration said in its 2017 National Drug Threat Assessment, however, that Mexican transnational criminal organizations transported illicit drugs into the US across its southwest border using varied methods.
"The most common method employed by these TCOs," it said, "involves transporting illicit drugs through US ports of entry in passenger vehicles with concealed compartments or commingled with legitimate goods on tractor trailers."
The 48 official land crossings that see the passage of millions of people, vehicles, and cargo every day — and are already staffed by law-enforcement and customs officials — also see the vast majority of illegal drug shipments.
The southwest US border, which stretches from San Diego to Texas' Gulf coast, "remains the main entry point for the majority of methamphetamine entering the United States," the DEA said in its 2017 report.
The report continued: "Methamphetamine seizures along the SWB increased 157 percent from CY 2012 (8,213 kg) to CY 2016 (21,121 kg). The majority (47%) of methamphetamine seized along the SWB in CY 2016 occurred in the San Diego corridor. Seizures increased in every corridor along the SWB."
Among the techniques smugglers use to conceal cargoes of meth are "human couriers commercial flights, parcel services, and commercial buses," according to the report. "Traffickers most commonly transport small, multikilogram shipments of methamphetamine in privately-owned vehicles."
The southwest border is "the key entry point for the majority of the cocaine entering the United States, according to US Customs and Border Protection data," the DEA report says.
"Traffickers most commonly smuggle cocaine into the United States via privately owned vehicles passing through ports of entry along the SWB. Cocaine is hidden amongst legitimate cargo on commercial trucks or secreted inside hidden compartments built within passenger vehicles."
Food and other perishable items are especially popular, especially because some goods, like raw fish, are pungent enough to conceal odors and deter curious customs officials. In one instance, the Sinaloa cartel chief Joaquín "El Chapo" Guzmán opened a cannery in Mexico to package cocaine in cans of chiles, which were labeled "Comadre Jalapeños."
"Commercial air smuggling is another important conveyance method for cocaine traffickers looking to smuggle cocaine from South America and the Caribbean into the United States," the DEA report adds. "This type of air smuggling has four different aspects to it: couriers, cargo, mail/express consignment, and internal conspiracy."
Couriers include people like airline passengers or crew members. Cargo shipments can range from a few kilos to a few tons hidden in commercial goods, like food or industrial equipment. Consignment shipments are more likely to move into and around the US in the mail. In other cases, airline or airport personnel on both ends of flights have conspired to traffic cocaine hidden in baggage or somewhere in an aircraft.
"Most of the heroin smuggled into the United States is brought overland across the SWB," according to the DEA, which notes that most of that is produced in Mexico or South America. Lesser amounts of South American, Southwest Asian, or Southeast Asian heroin are "transported by couriers on commercial airlines."
"The majority of any heroin that we seize is not between the ports of entry," Gil Kerlikowske, then the US Customs and Border Protection commissioner, told a congressional committee in spring 2016.
"It's smuggled through the ports of entry, whether is in San Isidro or El Paso, or whether is at JFK airport. Heroin seizures almost predominantly are through the port of entry and either carried in a concealed part of a vehicle or carried by an individual."
"We don't get much heroin seized by border patrol coming through," he added. "I think just because there are a lot of risks to the smugglers and the difficulty of trying to smuggle it through."
The DEA reported that heroin was often commingled with other drugs during transport, meth in particular. "Most heroin smuggled across the border is transported in small, multikilogram loads, in privately-owned vehicles, usually through California," the DEA report said, citing CBP.
Fentanyl, a synthetic opioid approved for use as an anesthetic and a painkiller, has become more common among US drug users. The extreme potency that makes it appealing to users also makes it dangerous to the people handling it, whether users or the police.
Some pharmaceutical fentanyl is diverted from healthcare facilities, though typically on a small scale and intended for personal use.
"Fentanyl is transported into the United States in parcel packages directly from China or from China through Canada, and is also smuggled across the SWB from Mexico," the DEA said in its 2017 report.
Large volumes of the drug are intercepted at the southwest border, though those seizures are typically of lower purity.
Smaller volumes of the drug arrive via mail from China, but those shipments are higher in quality and therefore more dangerous and more valuable.
"The fentanyl from China comes in two ways. One, through the use of the US postal system, which lags behind in terms of the technology that is required to be able to go through packages coming from foreign countries," Mike Vigil, the former chief of international operations for the DEA, told Business Insider in a spring 2017 interview.
"The second method of smuggling into the United States is that the fentanyl and the analogues flow from China into Mexico, into the drug cartels, and then across the US-Mexico border," Vigil added.
Like heroin or cocaine, a small of amount of fentanyl can fetch a high price. With "compact and expensive product," Adam Isacson of the Washington Office on Latin America noted last year, it's not surprising that "smugglers don't bother to transport it between ports of entry."
"Marijuana is the only drug covered in this assessment that is predominately smuggled between, instead of through, the ports of entry," the DEA said in its 2017 report.
"Large quantities of foreign-produced marijuana are smuggled into the United States via personally-owned vehicles, commercial vehicles, buses, rail systems, subterranean tunnels, small boats, unmanned aerial vehicles/drones, and catapults, and are walked across by backpackers," the report added.
Marijuana was for a long time a cash crop for Mexican traffickers. It was relatively easy to produce in abundance and didn't require a complicated refining process. If smuggled across the border in bulk, it could generate a tidy profit.
But with legalization, the dynamics of the marijuana trade have begun to shift.
Legalization in the US — in California in particular — has triggered a reverse in traditional smuggling patterns. When California dispensaries opened for recreational sales at the beginning of this year, Mexicans were in line, waiting to transport legally purchased weed back across the border.
"You are buying quality and a safe product," Roberto, one such customer, told El Universal.
Drug producers in Mexico's Golden Triangle — a hotbed for production of marijuana and opium and increasingly of synthetic drugs — have confirmed the declining appeal of Mexican marijuana. One self-described Sinaloa cartel operative said the price of a kilo of marijuana had fallen from about $74 in 2010 to a little more than $26 at the end of 2017.
"We keep sending chiva, perico, cristal," he told the Sinaloa-state-based newspaper Rio Doce, referring to heroin, cocaine, and meth, respectively. "The only one that decreased was mota," or marijuana.
If the ports of entry that dot the southern frontier are the frontline against the influx of illicit narcotics, then some of the personnel manning them are feeling overlooked.
Agents at the Laredo North port entry in Texas told the Associated Press earlier this year that they're undermanned and, at times, overwhelmed by the traffic at their checkpoint. Agents at the port have about 10 seconds to check the drivers of each of the roughly 9,000 vehicles they see a day and decide which ones to refer for further inspection.
The fiscal-year 2019 spending bill Trump signed earlier this year included about $50 million for new towers at the border, $87 million for remote video surveillance, and $20 million for ground sensors — total new spending on these items was a little less than $1.2 billion, a congressional aide told The Wall Street Journal.
But Customs and Border Protection is shorthanded and struggling to meet its personnel quota. As of March 17, the Border Patrol, which is a part of CBP, had 19,346 agents on duty, fewer than the 21,370 it is required to have. The agency has struggled for years to keep hiring even with the rate of agents quitting or retiring, according to CNN.
The Border Patrol has mounted a recruiting campaign across the US, touting the "fun" parts of the job, like riding ATVs and horses. "If you like to hike, you get paid to go out there and hike," a spokesman told Fronteras earlier this year.
"Our agents are understaffed and overworked," Hector Garza, the Laredo representative of the National Border Patrol Council, told the AP in February. "Even though they have all these forces against them, they go out there and try to do their best."