President Donald Trump has made building a wall along the southern border the backbone of his anti-drug policy to keep deadly narcotics like fentanyl from entering the country from Mexico.

But last month, as the president was delivering remarks at yet another public listening session on the opioid crisis, focusing his attention on a multimillion-dollar security investment on America’s southwest border, law enforcement officials in Canada announced they had shut down a massive flow of deadly narcotics coming to the U.S. from the opposite direction.

The trafficking operation, based in Calgary, Alberta—just a three-hour drive north of the Montana border—was capable of producing an estimated 18,000 counterfeit pills an hour for export to the U.S. and Canadian markets.

Cutting dyes on seized pill presses bore the stamps “80” and “CDN,” which are commonly associated with the prescription painkiller OxyContin. But there was no oxycodone (the active ingredient in Oxys) to be found. Instead, investigators from the Royal Canadian Mounted Police Clandestine Lab Enforcement and Response (CLEAR) Team discovered 18 kilos of suspected fentanyl in two different locations.

The investigation began in 2016 when police near Provo, Utah, pulled over a pickup truck carrying three men and 200 pounds of methamphetamine. Press reports at the time described it as the state’s largest ever meth bust, valued at $1.5 million on the street.

The men were all Canadian, and police would soon learn that meth trafficking was just a small part of the bilateral flow of drugs the group was moving across the U.S. border with Canada.

Had their trip been successful that day, the men would have continued traveling north on I-15, through Montana, and into Canada for their final stretch into Calgary. That’s where the leader of their group, Allistair Chapman—once a rising star in Alberta’s competitive amateur ice hockey community—had assembled a multi-national narcotics enterprise that exported counterfeit pills from Canada to the U.S. and returned home with cocaine and methamphetamine trafficked from Mexico. “Primarily this group acted as a wholesale drug distributor. We’re talking about large scale drug shipments at the multi kilo level,” said Staff Sgt. Barry McCurdy, a spokesperson for the Alberta Law Enforcement Response Team (ALERT) in Calgary, at a press conference on March 1 announcing the arrests of Chapman and five associates on drug and firearms charges.

At the time of the raid authorities said the pill presses were being used to manufacture steroids, but tests showed they were contaminated with fentanyl.

“By dismantling this lab we cut off a significant amount of fentanyl,” McCurdy said.

Investigators believe the group was also responsible for a double homicide committed in 2017 outside a Calgary shopping center that they believe was tied to a drug dispute.

The bust was the third major fentanyl seizure in Alberta in less than a year, and the second since January. Last July, police in Edmonton raided five homes in what was then-touted as the largest fentanyl seizure in Canadian history: 130,000 counterfeit pills along with two presses capable of producing 10,000 pills an hour. Then in January, rescue personnel responding to a house fire discovered 16 kilos of carfentanil—a powerful synthetic opioid believed to be 10,000-times more powerful than morphine—mixed with a cutting agent in the basement of another house in Edmonton. The powder was dyed pink and blue (indicating is was prepared to be pressed into pills).

“For the Edmonton Police Service, in respect to carfentanil, it’s the largest seizure that I’m aware of,” Inspector Shane Perka of the Edmonton Police Service told reporters after the bust. “This is a very substantial seizure.”

“ Last July, police in Edmonton raided five homes in what was then-touted as the largest fentanyl seizure in Canadian history: 130,000 counterfeit pills along with two presses capable of producing 10,000 pills an hour. ”

Some of that fentanyl is making it onto U.S. soil. From 2013 to 2016 fatalities linked to illicit fentanyl in the U.S. rose more than 500 percent; most of those who died, including the musician Prince, didn’t choose to take the drug.

A report this month indicates that Prince, who died in Minnesota (which shares a border with Canada) had “exceedingly high levels” of the synthetic narcotic in his system. Authorities found an assortment of counterfeit pills in the musician’s home.

Investigators have not revealed where the fentanyl that killed Prince came from or how he obtained it, but the Minnesota Department of Health has identified Canada as a primary conduit for Chinese-made synthetic opioids entering the state.

As The Daily Beast reported in 2016, in recent years Chinese labs have become a supplier of powerful fentanyl analogs designed to skirt U.S. law by modifying the chemical structure of the drugs. Last year China banned more than 100 of these analogs, and over the past two years the U.S. Drug Enforcement Administration has scheduled dozens of new novel opioids with close chemical structures to fentanyl. However they were unable to keep up with innovative clandestine chemists, and in February the DEA classified all chemicals with a structure similar to fentanyl under Schedule I of the Controlled Substances Act.

Canada is hardly a new player when it comes to satisfying demand for contraband in the U.S.

Long-established smuggling routes exist across America’s notoriously porous northern border, which has 120 points of entry, and stretches more than 5,500 miles—encompassing large areas of remote wilderness and numerous waterways.

“The Northern Border doesn’t always make headlines, but for too long it has been understaffed and there have not been sufficient resources to effectively combat drug trafficking and other crimes that can come across the border,” said Sen. Heidi Heitkamp (D-ND), who has sponsored legislation to strengthen security at the U.S.-Canada border.

During Prohibition, it’s estimated that 60-90 percent of booze entering the United States came from distilleries and breweries north of the U.S. border.

The border between Windsor, Ontario, and Detroit was a nexus of post-war drug trafficking; and until the early 1980s, heroin traffickers associated with fragments of the French Connection were still funneling large quantities of heroin from French-speaking Quebec to distribution networks in New York.

In 1987, federal prosecutors in Florida indicted 49 people in a massive cross-border conspiracy that was responsible for supplying 3.5 million counterfeit quaaludes to the U.S. market, or 70 percent of the illegal trade in the drug, according to prosecutors. And in 2008, authorities shut down a marijuana smuggling operation that had been shuttling hundreds of pounds of high-quality pot across the border from Ontario and into Western Pennsylvania disguised as commercial food shipments.

In recent years, Canada emerged as a global epicenter of synthetic and counterfeit drug manufacturing and processing—with everything from MDMA to fake Viagra flowing from clandestine labs north of the U.S. border. A 2005 State Department cable identified Canada as a “significant producer and transit country for precursor chemicals used to produce synthetic drugs,” and a “hot spot” of rising clandestine lab activity.

From 2012 to 2015 more than 500 pounds of MDMA was seized at the northern border, accounting for more than 90 percent of all Customs seizures of the drug.

“We are increasingly concerned about the multitude of routes of travel these illegal and ‘grey-market’ synthetic drugs are taking as they come into the region, and Canada is one route we feel bears watching,” said Jeremiah Daley, executive director of the Mid-Atlantic High Intensity Drug Trafficking Area (HIDTA), a program run by the Office of National Drug Control Policy. “While cross-border cooperation remains very strong with Canadian law enforcement, with so much focus being placed on our Southern Border, with good reason, we still need to be vigilant about threats coming from the North.”

In 2016 alone, U.S. Customs officials reported 2,015 drug arrests at land crossings at the U.S.-Canada border, while Canadian officials made more than 18,000 drug seizures. Trafficking groups routinely engage in so-called double exchanges in which designer drugs passed from Canada to the U.S. are exchanged for other narcotics, such as cocaine, for shipment back to Canada.

“ Trafficking groups routinely engage in so-called double exchanges in which drugs passed from Canada to the U.S. are exchanged for other narcotics like cocaine for shipment to Canada. ”

A dozen U.S. states share a border with Canada, including some of those hit hardest by the overdose crisis, such as New Hampshire and Vermont.

A State Department document published in 2011 describes the difficulty of policing the flow of drugs over these border crossings:

“The stealth with which both natural and synthetic drugs including marijuana, MDMA, and methamphetamine are produced in Canada and trafficked to the United States, makes it extremely difficult to measure the overall impact of such transshipments from this shared border country, although U.S. law enforcement agencies record considerable seizures of these substances from Canada.”

For years hockey bags have been described as a favored means of moving drugs from the U.S. to Canada, and in some cases they have been literally thrown across the border for pickup on the other side.

A story published in the Canadian news magazine MacLeans in 2009 refers to Canada as “The New Global Drug Lord,” citing data showing that more than 60 percent of the methamphetamine seized in Japan and more than 80 percent in Australia is synthesized in Canada.

While the fentanyl crisis is often treated like a monolith in the U.S. press, there are wide geographical variations in supply of the drug. Mexico remains the dominant supplier of illicitly manufactured powdered fentanyl in most major heroin markets, but the first wave of fentanyl overdoses following the crackdown on prescription-drug abuse in the U.S. was driven largely by a wave of adulterated pills, many of the them from Canada.

Part of the blame lays with the pharmaceutical industry.

When Purdue Pharmaceutical introduced a new abuse-deterrent OxyContin in the U.S. in 2010—which made it more difficult to crush for snorting and shooting—the original formulation remained on the market in Canada for another two years.

Smuggling of OxyContin from Canada to the U.S. spiked.

“I’m talking about trafficking organizations that are bringing in a thousand pills or so at a time,” said James Burns, assistant special agent in charge of the Drug Enforcement Administration’s operations in the state of New York.

Then, suddenly, OxyContin dried up in the Canadian market as well. In May 2013, just months after Purdue began withdrawing the drug from the Canadian market, authorities in Montreal seized 10,000 pills made of acetyl fentanyl in a microwave oven and toaster that were destined for Colorado. According to the Drug Enforcement Administration enough additional material was seized to make three million more pills.

The RCMP blames much of the trafficking on “criminal groups with connections to Asian source countries,” where the precursors for most synthetic drugs are sourced. The Criminal Intelligence Service of Canada says Asian gangs are especially strong in Vancouver, Calgary, Edmonton, and Toronto—all cities where fentanyl is endemic. According to published reports, the powerful “14K” and “Sun Yee On” triads are suppliers of precursor chemicals to Mexico’s Sinaloa Cartel.

Much of the focus is on transnational shipments of the drugs and their precursor ingredients from China. And Asian organized crime groups in Canada have been implicated in a number of cross-border drug trafficking schemes over the years. A 2011 report from the Department of Justice said Vietnamese and Chinese gangs produce “tens of millions of [MDMA] tablets for the U.S. market,” smuggling the drugs through border crossings in Washington, Michigan, New York, and Vermont.

Last year, when federal authorities in the U.S. unveiled their first indictment of Chinese nationals for trafficking fentanyl they traced shipments to from China via Canada. The investigation was launched following the death of an 18-year-old North Dakota man.

Five Canadians were arrested as part of the trafficking ring.

Fentanyl is easier to synthesize in a lab than MDMA, and Canadian syndicates are not only pressing pills but also manufacturing the drug.

Between 2011 and 2015, six clandestine labs were identified in Canada where illicit fentanyl production occurred or was intended to occur, according to Health Canada.

In 2015 authorities in Alberta seized 100 kilograms of the fentanyl precursor N-phenethylpiperidinone (NPP) at the Edmonton International Airport. They said the precursor was capable of producing 38 million fentanyl pills. The seizure led to a nine-month investigation dubbed “Project Alchemy” that ultimately turned up four kilos of the synthetic opioid W-18, 3,200 fentanyl pills, 2.5 kilos of methamphetamine, and more fentanyl precursor chemicals.

Canadian authorities are so concerned about transnational trafficking in designer opioids that they issued an advisory in January describing red flags for exposing money laundering tied to the importation of fentanyl or precursors used to make the drug.

The Department of Justice declined comment on the administration’s commitment to northern border security. However, the emerging threat of synthetic drugs trafficked from Canada has not gone unnoticed by officials in the U.S. In 2016, President Barack Obama signed the Northern Border Security Review Act, which was sponsored by Sen. Heitkamp and passed Congress with bipartisan support. As a result of the law, last year the U.S. government issued its inaugural “Northern Border Threat Assessment” identifying bilateral drug trafficking as the single greatest threat along the U.S.-Canada border.

The U.S. Customs and Border Protection Agency (CBP) has just one agent at the northern border for every nine patrolling southwest points of entry, despite the Canadian border being more than twice as long.

With fentanyl on its way to replacing heroin in most major drug markets, it’s not a matter of if, but how traffickers will get the synthetic opioid on U.S. soil. President Trump seems intent on closing one window for traffickers, but it will have limited effect as long as another, even bigger window, remains ajar.