The crisis over Greenland may deliver the moment when Europe must stand up to Donald Trump, as officials have said a US attempt to annex the territory could shatter the Nato transatlantic alliance.

European leaders have entertained Trump’s demands for nearly a year as he has pushed Nato countries to increase their defence spending to 5% of GDP, and threatened to pull US support from Ukraine as part of a peace process that appears to favour Russia. They have also given a muted response to US adventurism abroad including the capture and rendition of Venezuela’s Nicolás Maduro.

The obsequiousness has often played out in public. Various European leaders have vied for the role of “Trump whisperer” and Nato’s secretary general, Mark Rutte, infamously referred to him as “daddy” at a summit last June.

But Trump’s’ repeated and increasingly bellicose demands that Denmark cede or sell him semi-autonomous Greenland has sparked one of the greatest crises for transatlantic partnership in its history – and may force Europe to draw a line in the snow.

“The president’s ambition is on the table,” the Danish foreign minister, Lars Løkke Rasmussen told Fox News after the talks. “Of course we have our red lines. This is 2026, you trade with people but you don’t trade people.”

After an hour-long meeting with the US vice-president, JD Vance, and secretary of state, Marco Rubio, Rasmussen and Greenland’s foreign minister, Vivian Motzfeldt, stood grim-faced smoking cigarettes outside of the Eisenhower executive building in Washington DC.

“When it comes to Greenland, the Europeans have found a red line that they really want to stand by,” said Kristine Berzina, a senior fellow at the German Marshall Fund for US defence and transatlantic security.

“Everything else has been subject to negotiation … but the Greenland situation is different because it comes to the question of sovereignty, and it comes to the question of whether Europe is capable of standing up for itself in terms of its own territory, its own rights.”

Europe, however, was at a “diplomatic disadvantage” because of its dependency on the US for security, said Latvia’s former prime minister Krišjanis Kariņš.

“Europe is not, unfortunately, in a strong position to strongly object, because, say, if Europe were to open up the dispute into the trade area, I’m certain that the US would respond in kind or more than in kind,” he said. “At the end of the day, Europe still needs the US.”

The strain on officials from Denmark and Greenland has been enormous. A day after meeting US officials, a visibly emotional Motzfeldt said she had been overwhelmed by the last few days of negotiations.

“Denmark has really only been a good ally to the US,” said Marisol Maddox, a senior fellow at Dartmouth University’s Arctic studies institute. “So that’s also a part of what makes this so extraordinary, is this was like going up to your best friend and just randomly slapping them in the face … There’s nothing to provoke this.”

Trump’s interest in acquiring the island has only grown since his longtime friend Ronald Lauder, the heir to the Estée Lauder cosmetics company, first suggested it to him in 2019. The White House has said its main concern is national security, but Trump has admitted that ego plays a key role as well. He told the New York Times last week that owning Greenland was “what I feel is psychologically needed for success”. On Friday, Trump threatened to impose tariffs on countries that do not “go along” with his ambition to annex Greenland.

Others in his administration – particularly Vance – have seen the obsession over Greenland as an opportunity to pick another fight with European allies, and European diplomats saw his decision to join the negotiations as a negative sign.

Vance “is especially enjoying this”, one said. “It’s clear why he’s gotten involved and it will make the talks more emotional.” Politico reported that 10 ministers and officials polled on his involvement did not regard him as an ally on Greenland or other transatlantic matters.

Europe has responded by seeking to cut the legs out from under the Trump administration’s argument that Greenland is underprotected from a potential Russian or Chinese attack. A small French military contingent arrived on the island on Thursday as part of a limited deployment including troops from Germany, Sweden, Norway, Finland, the Netherlands and the UK.

“The defence and protection of Greenland is a common concern for the entire Nato alliance,” said Denmark’s prime minister, Mette Frederiksen. Rasmussen and Motzfeldt are scheduled to meet Rutte for talks on Monday.

By deploying troops and assets, Kariņš said European leaders could take away a pretext of the Trump administration for annexing the territory, referring to arguments that it was not protected from Russian and Chinese aggression.

“President Trump has a pretty established track record now of sort of doing things his own way,” he said. But if Europe strengthens Greenland’s military security, “it takes away a public argument by the Trump administration” for annexation.

Aside from military deployments, observers have plenty of ideas about how the EU can protect Danish sovereignty of Greenland and assert European interest. At the milder end, suggestions include convening an international summit on Arctic security in Nuuk, co-organised by Denmark and Greenland, together with the EU and non-EU countries including the UK, Canada, Norway and the US.

More radical ideas are also circulating, such as freezing the European parliament’s vote on ratification of the EU-US trade deal agreed with Trump at his Turnberry golf resort in Scotland last year. A group of socialist and green MEPs argue that voting on the deal, currently scheduled for February, would be “easily seen as rewarding … his actions”.

Such a move, however, is unlikely to gain majority support in the right-leaning parliament, where many MEPs are wary of antagonising the White House.

The day after Rasmussen said Trump remained intent on conquering Greenland, EU officials continued to be diplomatic. The European Commission president, Ursula von der Leyen, described the US on Thursday as an ally and partner while discussing the Greenland situation.

She also set out how the EU was seeking to deepen support for the island, citing the opening of an office in Nuuk and a proposal to double EU financial aid. “Greenland can count on us, politically, economically and financially,” she told reporters.

Constantinos Kombos, the foreign minister of Cyprus, which currently holds the EU’s rotating presidency, said the bloc needed to intensify dialogue with the US over Greenland. “Maybe [the current administration] is different than what we are used to and it is, but that doesn’t mean we have the luxury of responding with our self-isolation,” he said.