MANCHESTER, N.H. — Former President Donald Trump described the U.S. border as “not so hot.” Florida Gov. Ron DeSantis said it’s the site of a worsening problem. And Nikki Haley, the former U.S. ambassador to the United Nations, said she would do whatever it takes to stop illegal crossings there, up to and including building a massive wall.

The rhetoric wouldn’t be out of place for Republicans in reference to the U.S. border with Mexico, a staple of Republican campaign speeches and the site where Customs and Border Protection apprehended more than 2.4 million people who entered the country illegally from October 2022 to September.

But those remarks weren’t about the southern border. Rather, they were about the border with Canada.

As Republican voters time and time again rate immigration as a top-three issue facing the country, GOP presidential candidates are increasingly bringing the northern border with Canada to the political forefront. In New Hampshire, the site of the first-in-the-nation primary and a state that shares a border with Canada, that focus has been turned up a notch.

Before he dropped out of the race two days ago, DeSantis pledged to New Hampshire voters Friday that he would provide increased resources to bulk up protection at the northern border, blaming President Joe Biden for what he sees as a problem that’s getting worse.

Trump made his comment about the northern border’s being “not so hot, either,” at a stop in Iowa this month, adding that he “started to use that” in discussing immigration and border security. At a rally for Trump in Concord on Friday, Rep. Elise Stefanik, R-N.Y., described “a skyrocketing of illegals crossing our northern border,” including some, she said, who were “on the terrorist watch list.”

But no one has talked up northern border security more than Haley, who has mentioned the border with Canada at numerous campaign stops in New Hampshire over the past week.

During a CNN town hall in Henniker on Thursday, Haley said that “we don’t talk enough about the northern border,” saying hundreds of suspected terrorists were being apprehended there.

Customs and Border Protection statistics show nearly 500 people on the terrorist watch list were apprehended at the northern border from October 2022 to September, compared to 80 on the southern border.

Speaking to reporters Saturday at an event in Peterborough, Haley promised to “do whatever it takes to keep people out.”

“We will do a wall,” she said. “We will do any sort of border patrol that we need to have on there. Whatever it takes to keep people out that are illegal from coming in, we will do it.”

Apprehensions at the northern border have increased over the past three fiscal years, though they are a mere fraction of the apprehensions at the southern border. Compared to the more than 2.4 million encounters there, CBP recorded roughly 189,000 apprehensions at the northern border. But that was a substantial increase from the previous fiscal year — when nearly 110,000 apprehensions took place — and fiscal year 2021, when about 27,000 were recorded.

In the Swanton Sector, which includes New Hampshire, Vermont and parts of upstate New York, 6,925 people were apprehended from October 2022 to September, a substantial increase over the 1,065 apprehended the previous year.

New Hampshire Gov. Chris Sununu — who has campaigned across the state with Haley — late last year announced a tenfold increase in patrols along his state’s border with Canada. But most voters here said in a recent survey that they weren’t concerned about the northern border.

A Suffolk University/Boston Globe/USA Today poll of New Hampshire voters this month, which showed widespread concern about the number of migrants entering the country, found that just 37% were concerned about the northern border, while 61% weren’t. When the results were limited to Republicans, 64% said they were concerned, while 32% said they weren’t.

Maria Martins, a Trump supporter from Manchester, said she thinks immigration is “a huge issue.” But she was less sure of any crisis developing to her state’s north.

“I personally haven’t noticed it,” she said. “But to me, it doesn’t matter where they’re coming from. They have to be prepared to support themselves.”

Julie Smith, a New Hampshire voter backing Trump, said she thinks the northern border should be of greater focus for lawmakers.

“I don’t think it gets enough attention,” she said. “But again, I’m not there. I just think that law should be enforced.”

In a Republican primary in which candidates have unified around militarizing the borders, completing the border wall Trump began in his first term and conducting large-scale immigration raids and mass deportations, Democrats say the focus on the northern border is merely the latest GOP attempt to gin up fears among its right-wing base as an election nears.

A national Democratic strategist, speaking on condition of anonymity without authorization to speak publicly, said the latest pitch brought back memories of migrant caravans that were a focus of conservative media news cycles ahead of recent elections.

“You know, Vivek [Ramaswamy] tried this,” this person said, noting that his focus on the northern border didn’t boost his candidacy. “This is the same playbook that [Republicans have] tried over and over, and it has failed over and over.”

Ramaswamy, the businessman who ended his presidential campaign and endorsed Trump after a fourth-place finish in Iowa, was the first candidate to bring a sustained focus on the border with Canada. At an NBC News debate in November, he said: “Don’t just build the wall; build both walls.”

Before he dropped out, Ramaswamy made a campaign stop in Pittsburgh, New Hampshire, which sits along the rocky border, to visit it firsthand. And at his final campaign rally in Iowa last week, he said he would “use our own military to secure our own borders in the United States of America, southern border and northern border.”

The issue isn’t entirely new for Republicans. Early last year, more than two dozen House Republicans formed the Northern Border Security Caucus.

Matthew Knoedler, a spokesman for Rep. Mike Kelly, R-Pa., a co-chair of the caucus, wrote in a message that Kelly “is encouraged to see that candidates in the 2024 presidential race are also focusing on the real needs along America’s Northern border as well as our Southern border.”

With Senate negotiators working on a bipartisan immigration package that has Biden’s blessing, change could soon be coming for both borders. What’s more, in March, the Biden administration struck a deal with the Canadian government allowing both countries to turn back asylum-seekers who crossed their shared border.

In a statement to NBC News, a Customs and Border Protection spokesperson sought to discourage people from illegally crossing into the U.S. from Canada.

“There are very real dangers involved in crossing the international border between the U.S. and Canada,” the spokesperson said. “No matter what smugglers say, those who do not have a legal basis to remain in the country will be removed and people should not make the dangerous journey. Especially as the weather changes and winter is upon the North Country, it’s dangerous to attempt to try this trek.”

Reached for comment, a spokesperson for the Canadian Embassy to the U.S. said Canada “is working with its closest friend and greatest ally, the United States, to strengthen the protection of our shared border — land, air and waterways.”

“As threats at the border evolve, Canada continues to make significant investments to reinforce our shared border,” the spokesperson continued. “We are actively collaborating with U.S. counterparts to share intelligence and to detect and intercept unlawful activity at the earliest opportunity. Our countries share the same objective: keeping the border open to legitimate trade and travel but closed to terrorists, criminals and threats to citizen health and safety.”