The shortest flight path from Russia to the United States would take an enemy bomber over the North Pole and across Canadian airspace. During the Cold War, that simple fact was the impetus for the creation of the North American Aerospace Defense Command, or NORAD, which forged an integrated radar network across the two countries, effectively treating North American airspace as a single defensive zone.

Today, there’s less concern about a Russian barrage landing on U.S. soil, but NORAD remains relevant. Russian bombers still fly near Alaska and the Canadian Arctic. China’s expanding nuclear arsenal poses its own threat. Other airborne objects require vigilance, a lesson underscored by the mysterious flight path, in 2023, of a Chinese spy balloon, which NORAD shot down. This should matter to President Trump, who has identified the Western Hemisphere as a security priority.

He even has a name for his approach: the “Donroe Doctrine.”But all is not well at NORAD, the world’s only binational military command, headquartered at the Peterson Space Force Base in Colorado Springs. NORAD, which was founded in 1958, now demonstrates how the president’s disdain for U.S. allies risks undermining the military cooperation that has kept the United States safe for decades.

Positions at NORAD and other integrated combatant commands in the United States used to be plum posts for ambitious Canadian military officers, giving them a chance to coordinate with Americans on intelligence, air and missile defense, and joint operations. That’s changing. U.S. and Canadian officials told me that Canada has lately struggled to find senior officers willing to take the jobs, a problem acute enough that Canadian officers have shared their concerns with counterparts in Colorado Springs, Ottawa, and Washington.

The reasons are threefold, according to current and former officials who described the dynamic to me on the condition of anonymity in order to address a sensitive subject. Although the influence and sophistication of the U.S. military once made the postings desirable to ambitious officers, some now fear that time in the United States might hurt their chances for future promotions if relations spiral further out of control. They also see diminishing returns from a posting in which they’re likely to have their access curtailed as a byproduct of political tensions. And they face resistance from their families, who worry that anti-Canadian sentiment whipped up by Trump might make the country inhospitable, even temporarily.

Canadian officers considering U.S.-based posts don’t believe that they’ll be treated as equals, according to several who spoke with me. While the Trump administration has bullied and threatened numerous allies, these officers perceive particular hostility toward Canada—in part because of the vehemence of the trade dispute, and in part because Prime Minister Mark Carney has been willing, at times, to stand up to Trump. “If you’re a two-star general in Canada, and you’ve got maybe one or two extremely important jobs left in your career, will you use one of them to take up a position in the States, where you might be underemployed, with little access and little meaningful work to show for it?” one Canadian officer asked.

Some of the officials I spoke with noted that strained relations had not yet caused a tactical breakdown—no one had taken their eye off radar scopes or infrared cameras. And that’s what a NORAD spokesperson emphasized in response to my questions, issuing a statement saying that high-level Canadian roles at the binational command “remain fully staffed and highly regarded as career-enhancing opportunities, with Canadian personnel and their families fully integrated and operating with the systemic access required to execute binational defense operations for the homelands.”

The true impact of Canadian reluctance to serve in the United States may become manifest only in a crisis. In addition to the essential national-security functions performed by NORAD, the command also fosters camaraderie between the ranks of the two militaries. That’s vital if the U.S. military should ever need to project force to the north, including by moving personnel across Canada. Several of the people I spoke with raised the prospect of a conflict with China, which would quickly threaten Alaska, a crucial strategic hub.

Moving U.S. forces to the noncontiguous state would depend on Canadian cooperation. In such a situation, Washington would want Canadian commanders who have served in the United States, so that American officers aren’t building new partnerships but are depending on people they’ve known for years. Canadian generals who’ve passed on postings in the United States because of friction between the two countries are much less likely to be sympathetic.

Since he returned to power last year, Trump has alienated longtime allies while praising rogue states such as North Korea. He has called Germany a “broken country” and said that French President Emmanuel Macron “always gets it wrong.”As a group, European leaders earned the epithet “weak.”He has imposed steep tariffs on their countries and threatened a foundation of Western security by raising doubts about U.S. fidelity to Article 5 of the NATO charter—that an attack on one is an attack on all.

Still, when I speak with senior officers in various allied countries—even Denmark, where the armed forces prepared for a possible U.S. invasion of Greenland, earlier this year—they maintain that military-to-military cooperation continues despite political disagreements. Canada may be the first place where that is cracking. “The day-to-day relationship has deteriorated,” David Perry, an Ottawa-based defense analyst, told me. “There’s been a tangible change in the way the two countries interact on defense and security.”

That Washington is now choosing to alienate its northern neighbor is ironic because Canada, like other NATO members, is in the process of investing in the type of hard power that will make it an even more useful ally. When I met with Canada’s defense minister, David McGuinty, in February, the government had just released its first defense–industrial strategy, a plan to get weapons faster and—given geopolitical strife—to get more of them from Canadian suppliers.

“Obviously continuing to work with the U.S.,” McGuinty said, “but now much more expansively looking to diversify.”Earlier this year, the Canadian government promised to review whether to move forward with a full order of F-35 stealth fighters, which are produced by Lockheed Martin. This month, the government paused its acquisition of U.S.-made Black Hawk helicopters because of trade and diplomatic friction with Washington, according to CBC News and Radio-Canada. Canada is spending billions to upgrade radars, sensors, and other systems.

Its participation in Trump’s proposed “Golden Dome” would extend and strengthen the defensive shield, with the potential to protect both countries. But it’s hard to put much faith in protection from a bully. “Trust is easy to lose and hard to build,” Christopher Sands, the director of the Center for U.S.-Canada Studies at Johns Hopkins University School of Advanced International Studies, told me.

The current rancor is entirely different from past trade disputes, which have often been combative—“like a courtroom drama,” Sands said. But the fighting once stayed out of public view, managed by low-profile diplomats. Now the public is in the audience and can’t look away from the president’s antics, which have “poisoned people-to-people relations.”The armed forces couldn’t remain immune forever.

An executive order on Trump’s first day back in office, in January 2025, made Canadian officers wonder whether the U.S. military might be used against them. The order assigned U.S. Northern Command, which shares NORAD’s Colorado headquarters, to the mission to “seal the borders and maintain the sovereignty, territorial integrity, and security of the United States.”It did not specify the southern border, causing Canadian officials in Colorado to ask their counterparts, as relations worsened over time: Are you planning to militarize the northern border, one of the world’s longest undefended and peaceful frontiers? U.S. officials tried to reassure them that any action would be cooperative.

But the guarantee of cooperation became difficult to sustain. Defending new tariffs imposed on Canada in February 2025, Trump wrote on social media that “Canada ceases to exist as a viable Country” without U.S. support. “Therefore, Canada should become our Cherished 51st State.”Early on, references to Canadian statehood had elicited laughs during staff meetings at NORAD. But the mood soon changed. In April, Trump rebuffed the suggestion that his talk of annexation was just bluster. “I’m really not trolling,” he said in an interview with Time.

By the end of the year, jokes within the binational command about the 51st state were met with silence or curt rebuttals. Attitudes had shifted dramatically. An Angus Reid Institute poll found that almost half of Canadians said that their government should view the United States as an “enemy” or “potential threat,” while only 27 percent called Washington a friend and ally. Canadian officers serving in the United States divulged to colleagues that their families didn’t want to visit them over the holidays, because they were afraid of crossing the border or encountering animosity in American communities.

In addition to the joint command in Colorado Springs, Canadian generals have served as deputy commanders of U.S. Army corps in North Carolina, Texas, and Washington State.

Defense Secretary Pete Hegseth’s approach was even less subtle. In August, he posted a photo of two young female Canadian cadets. Their physical appearance seemed not to impress him; he captioned the photo “this is real.”The post stunned Canadians for its crassness and unprofessionalism. Wayne Eyre, who served as chief of Canada’s defense staff from 2021 to 2024, told me that he found Hegseth’s intervention “highly insulting.”

It was followed, the next month, by a cartoon image that Trump circulated on his Truth Social feed of him beating Carney with a hockey stick—“unimaginable conduct by the president of the United States, even in our most dystopian imagination,” as one Canadian official put it to me. U.S. military leaders at NORAD have tried to put on a brave face, reporting to visitors that binational cooperation is continuing unimpeded. But away from the spotlight, Canadian officers will acknowledge the strain, current and former officials told me.

Eyre warned that cooperation of the kind that he helped oversee is more vulnerable than it might appear. “It’s sad, disappointing, and disturbing to see that deep relationship come under attack,” he said. “In my view, it’s a case of the U.S. undergoing self-harm by discarding and calling into question its competitive advantage, which is this system of alliances.”Most of what the public knows about NORAD comes from its Santa Tracker, a lighthearted simulation of Santa Claus’s journey around the world on Christmas Eve. That’s because the command’s real business—guarding the skies—is mostly invisible. That is, until it stops working.