While much has been made of the apparent security threat emanating from beyond America’s southern border by the White House and elsewhere, recent events show that it may actually be Canada that presents a greater terror concern to US soil.

During the first six months of 2018, six foreign individuals listed on the Terrorist Screening Database were stopped while attempting to enter the country from Mexico, according to US government officials. At the Canadian border? Forty-one people.

And while more than 16,000 patrol agents are deployed at the Mexican border, with thousands more on the way, just 2,097 monitor the Canadian frontier, which spans 8,900 kilometres – more than the distance from London to Sri Lanka. In January, news website Politico reported that as many as 200 US border patrol positions on the Canadian border went unfilled.

Since 2015, four residents of Canada have been charged with carrying out or conspiring in terror-related attacks on US soil. In 2015, a Tunisian citizen living in Montreal and a Palestinian from Toronto were sentenced to life in prison for plotting to derail a passenger train travelling between Ontario and New York.

Last December, a 20-year-old man from Mississauga, outside Toronto, was sentenced to 40 years in jail for attempting to plant explosives on the New York subway and in Times Square. Abdulrahman El Bahnasawy, who suffered mental health and addiction problems, was believed to have been in direct contact with ISIS elements in Pakistan and the Philippines.

One month later, police found an “explosive substance” at the home of a 16-year-old youth in Kingston, a Canadian town on the US border, following a tip off of a “substantial and credible attack plot” from the FBI, though police haven’t revealed whether US targets were threatened.

Perhaps the most unusual case surrounds Amor Ftouhi, a married father of three and truck driver from Montreal, who attacked and seriously injured an on-duty police officer with a knife at an airport in Flint, Michigan in June 2017, after driving 1,600km across the border.

New York police stand guard in Times Square.

Ftouhi tried and failed to buy automatic weapons in Michigan before the attack and is not believed to have been affiliated or directed by any group. In court, his lawyers recounted how he struggled financially in Canada and felt discriminated against at work for not being allowed to take prayer breaks and for refusing to deliver alcohol.

“I will not accept for myself the humiliation and shame as I see Muslims afflicted with what I am afflicted,” he wrote in a will addressed to his wife and found at his home following the attack. The will clearly shows that Ftouhi expected to mount a suicide mission; at his sentencing to a life in prison term last April, he refused to repent for his actions.

After emigrating from Tunisia in 2007, Ftouhi lived on rue Belair in the heart of Montreal’s ‘Little Maghreb,’ a four-minute walk from the nearest mosque and the Centre Communautaire Musulman de Montreal, a community centre. (Calls and messages left with the Centre by The National seeking comment on whether Ftouhi was known in the area went unanswered.)

While little is known about how Ftouhi became radicalised, Montreal is home to more than 65,000 immigrants from Algeria, Tunisia and Morocco, attracted in part by the city’s Francophone character. These communities are not particularly susceptible to radicalisation, says Hicham Tiflati, a Montreal-based radicalisation expert studying Canadian foreign fighters.

But he says the city has “a few radicalised ‘agents’ with radical ideology”.

One is Adil Charkaoui, a Morocco-born radical known for espousing extremist views and who was arrested and held under a security certificate in 2003.

“(Charkaoui) has a mosque and in his Friday sermons you might hear terminology and tones of his lectures (in which) he was indirectly pushing youth (to violence),” says Mr Tiflati. “He would say things like: ‘you are not a real man, not a real woman, not a Muslim when Muslims are dying in Syria and Iraq, and you’re not doing anything about it.’”

The expert says it is thought that Charkaoui was a main reason that seven young men from Montreal’s North African community, several who attended a community college where Charkaoui had briefly rented a room to teach, went to Syria to fight with ISIS in January 2015. Around 185 Canadians travelled to fight for ISIS and approximately 60 of those have returned to the country, according to The Soufan Group, a US intelligence firm.

Yet experts say the number of people living in Canada that represent a significant threat to the US is believed to be very small. Of the six charged with planning terrorist activities in America over the past two decades, only three have succeeded in entering the country. Just one, Ftouhi, was successful in carrying out an actual attack, and even that proved to be non-fatal.

“There are different levels of risk. Yes, we’ve had some individuals from Canada who have attempted to enter the United States or succeeded, but in terms of the volume it’s still relatively small,” says Theresa Brown, director of immigration and cross-border policy at the Washington-based Bipartisan Policy Center. “Our intelligence and law enforcement cooperation with Canada is very high.”

Still, while the terrorist threat may not be a significant concern for some, the broader picture shows that the number people detained while trying to illegally enter the US from Quebec has almost trebled in the last four years. When Ftouhi drove across the border at Champlain, New York en route to carrying out his attack, he was not on the watchlist of Canadian or US intelligence authorities, or the FBI. Nor was he known at the time to Montreal’s Centre for the Prevention of Radicalisation Leading to Violence, a non-profit.

Relations between the intelligence agencies of both countries were close under the Obama administration and three years ago, they signed a declaration to work together against mutual terror threats, although Canada is said to have dragged its feet in information sharing due to concerns over privacy and data sharing.

Ms Brown says there are initiatives including a binational law enforcement task force and a host of other cooperative border efforts that are coordinated between the countries. “People who have become radicalised at some point are unknown to the government until they do something,” she says.

“That is the big security threat. Canada and the United States share that.”