STANSTEAD, Quebec — For some folks living in a cluster of small towns straddling the U.S.-Canadian border here, life could not feel more comfortably secure.

Six Canadian and U.S. checkpoints service the 2½-mile stretch of frontier that cuts through the villages of Derby Line and Beebe Plain, both in Vermont, and the town of Stanstead, in Quebec. Street cameras, satellite and sensor surveillance, vehicle patrols, and the occasional thumping helicopter overhead ensure that residents can’t budge without someone watching.

It’s no wonder that many don’t bother to lock their doors.

“We really feel safe,” said Laurie Dubois, 56, an American living on the Canadian side. With the cameras and the Royal Canadian Mounted Police, she noted, “there’s not a whole lot of bad stuff going on.”

But the heightened security is a sign of the times that doesn’t sit well with all of the residents in these once close-knit cross-border communities tucked into the northern highlands of the Appalachian Mountains.

“It’s a pretty pain in the ass is what it is,” said Patrick Boisvert, 75, a machinist in Beebe Plain with a mathematics degree from St. Michael’s College, in Vermont.

Surveillance has grown stricter and more intrusive all along the 3,900-mile lower-U.S.-Canadian frontier since Sept. 11, 2001, creating a continent-wide gulf that many argue reflects a political parting of ways, as well – American conservatism vs. Canadian socialism, as defined by Canada’s universal health care, maternity leave, tough gun laws, and subsidized day care and higher education.

But the burden borne by the Vermont-Quebec communities is unique. Residents linked by intermarriage, blood relations and, in many cases, dual citizenship are now separated by an invisible but hardening wall. Neighborhoods that once shared schools, sports facilities, doctors and churches in a kind of free-flowing human commerce have retreated to their own sides of the border.

Nowhere is the divide more apparent than along the 620-yard stretch of Highway 247 — called Canusa Street in Vermont and Rue Canusa in Quebec — where Boisvert has lived all of his life.

On Canusa, the border runs east-west more or less right down the middle of the street. Drive on the north side, going west, and you are in Canada. Drive east and you are in the United States.

Boisvert’s father was a Canadian born in the small town of Rock Island (now Stanstead) just across from Derby Line. He married an American and moved to the white clapboard house in Beebe Plain where Patrick Boisvert still lives with his wife, Louise.

Boisvert said that when he was a child, his best friend was a Canadian who lived across Canusa Street. “So, hell, we were back and forth across that road 100 times a day. We didn’t think about it. Border? What border? And now this s— that’s going on.”

What Boisvert means is that every time he or his wife cross the street or drive off on an errand, they have to report in at the U.S. or Canadian border posts. It’s the same for all 23 families on the street.

The border stations are close by, but often there are lines. The fine for not checking in is a steep $5,000 and/or two years in jail on the American side and 1,000 Canadian dollars on the Canadian side. And there’s no escaping the surveillance, Boisvert said.

Louise said she no longer visits her Canadian neighbor Mylene.

“If we are going to talk to each other, she stands on her side, and I stand on mine,” she said. One time, “there was some sort of little domesticated rat that was following Mylene around over there and she came over, she had her passport in her hand, and she said, ‘There’s this rat, and I think it’s somebody’s pet.’ She wanted to find the owner. But she had to go and report and come over here and then she was going to have to go to the Canadian side to report back. … I don’t know what happened to the rat.”

Metal gates now block the north-south streets that once connected Derby Line and Stanstead.

In at least two cases, the border runs through homes, restricting access to back yards and forcing owners to seal off doors.

The Haskell Free Library and Opera House famously straddles the Derby Line-Stanstead frontier. A row of flowerpots denotes the border traversing the street that leads to the front door, which is in the United States. Most of the rest of the building is in Canada. Inside, black tape tracing the border runs diagonally through the children’s section.

Here the border rules fall away. Canadians and Americans are permitted to access to the century-old brick building without having to check in with the border guards. Children enchanted by Peter Pan find their own version of Neverland.

Dual citizenship is common — a result of marriages and also the fact that many Canadians were born just across the border at the hospital in Newport, thus acquiring U.S. citizenship.

Where these people opted to live often reflects the divergent political and social paths the two countries have chosen.

Laurie Dubois immigrated to Canada from Vermont in 1971, when her mother married a Canadian. Now she and her American husband operate a small cross-border business engraving tombstones. The area’s granite quarries are a mainstay of the economically struggling region.

She said she would like to move back to the United States, because “Americans are more friendly,” but stays because of Canada’s social safety nets, particularly its universal health care.

“It covers a lot of stuff that my husband deals with,” she said. “He has a heart problem, and he has an ileostomy. He has kidney problems.”

For Louise Boisvert, Democratic presidential candidate Bernie Sanders “is our babe” because he wants to bring Canada’s subsidized higher education, single-payer universal health care, higher minimum wage and paid maternity leave to the United States.

“It’s time we started looking after our citizens,” she said.

But her husband says Sanders is “delusional” if he thinks the United States will adopt universal health coverage.

“I don’t think you can change it,” he said. “Everything is too entrenched.”

With each generation, memories of a closer cross-border community have faded. Sylvain Matte, 43, is an engineer and machine designer who lives up the street from the Boisverts on the Canadian side.

He notes that he has had casual exchanges — barbecues and drinks around a bonfire — with his American neighbors, but nothing that approaches real friendship.

“For me, it’s normal,” he said of the street.

His 18-year-old daughter, Vladimire, added that she had an American friend when she was small, but not anymore.

“Americans are different,” she said. “I can’t really put my finger on why, but they are.”