President Donald Trump speaks to media before boarding Air Force One at Morristown Municipal Airport, in New Jersey on Sunday. Credit:AP Days later, he'll sit down with Russian President Vladimir Putin for their first one-on-one summit. European leaders worry that Trump could bargain away their security in the name of better relations with the Kremlin. European Council President Donald Tusk warned European leaders last month that judging by Trump's language, allies could no longer assume that NATO would endure. NATO diplomats are making dark jokes about whether Trump and Putin could unveil a globe-shifting alliance of the sort that helped lead to World War I. Others are considering the legal architecture for a NATO in which the US is no longer the preeminent player. US President Donald Trump meets briefly with Russian President Vladimir Putin at the G20 Summit in Hamburg last year. Credit:AP "The biggest of the allies doesn't just have a disagreement with us, but he actually seems willing to walk away," said Tomas Valasek, a former Slovak ambassador to NATO who runs Carnegie Europe, a Brussels think tank. "Deterrence has already been broken."

Such sentiments are based on Trump's words and actions in recent weeks, as he has more fully embraced his own plate-breaking instincts on foreign policy after a first year of being held back by more conventional aides. Few believe that Trump would actually withdraw from NATO - at minimum, they think he would be restrained by Republican partners in Congress. But they worry about moves that could initiate an unravelling. Europeans fear a repeat of last month's Group of Seven summit in Canada, when Trump fought with leaders of Washington's closest allies, then withheld his signature from the bromide-filled declaration that comes out of such meetings as a matter of course. Loading Only this time, there could be immediate security implications. "It's one thing if he goes to the G7 and is rude to people," a senior NATO diplomat said. "It's another thing to derail NATO."

Europeans are "scared" that Trump could trigger a crisis, said another senior European official, adding an off-colour word for emphasis. Trump has already said he is looking for a fight. "I'm going to tell NATO - you got to start paying your bills. The United States is not going to take care of everything," Trump told a rowdy rally in Montana last week. "We are the schmucks that are paying for the whole thing." Last month he sent letters to leaders whose countries are not living up to their NATO defence spending pledges, warning that the US might cut them off if they don't pour more money into their militaries. And he has questioned why the US should run a trade deficit with nations it is spending money to protect, suggesting he could use security guarantees as a bargaining chip in trade talks. A protester marches next to giant puppet of US President Donald Trump as he holds a sign which reads 'Pro-America, Anti-Trump' during a demonstration in Brussels on Saturday. Credit:AP

Europeans say the angry rhetoric is already damaging alliance security, since part of deterring Russia and other potential adversaries requires leaving no doubt that if a single member is attacked, every country will come to its aid. But leaders and diplomats worry that Trump could soon go further to undermine the alliance. They are concerned he could halt US participation in military exercises in eastern Europe to avoid "provoking" Russia, since he made a similar concession about joint exercises with South Korea after his meeting with Kim Jong-un. They fret he could draw down the US military presence in Europe, a move that could poke holes in the US security umbrella that reaches up to Russia's border. Their nightmare is that Trump could embrace Putin at their summit by recognising Russia's annexation of Crimea, emboldening nations around the world to redraw borders by force. "It's such a fundamental issue," said a senior NATO diplomat. "It would legitimise a whole range of actions. If you have the power, the raw conventional military power, you can do what you want." Large crowds in Lenin Square to celebrate the preliminary results of the Crimean Referendum, that in effect ratified the annexation of Crimea. Credit:Kate Geraghty

"Now I'm depressed," the diplomat added. "The fact that we're even thinking about it." The US diplomats negotiating the substance of the agreements ahead of the summit say they have received no instructions that would depart from decades of US foreign policy. On paper, at least, Trump is set to condemn Russian behaviour in Ukraine, endorse collective defence and sign off on a range of new plans that would expand US military activity in Europe, not diminish it. "This is a very substantive and meaty summit," the US ambassador to NATO, Kay Bailey Hutchison, told reporters last week. "NATO is doing many of the things that the president has asked them to." But Trump himself appears to want to take a different direction. At last month's G7 summit, he suggested that the 2014 annexation was legitimate because most residents of the Crimean Peninsula were Russian-speaking. Leaders pushed back hard but did not feel as though they made headway, according to a person who was in the room at the time. Recognition of Crimea would undermine the basis of Western action against the Kremlin since 2014, including sanctions and the strengthening of NATO along the Russian border. It would violate US commitments to Ukraine, since Kiev received guarantees in 1994 that Washington would protect its territorial integrity in exchange for Ukraine's giving up Soviet-era nuclear stockpiles.

And it would be a moral blow to NATO. President Donald Trump jokes with British Foreign Minister Boris Johnson as British Prime Minister Theresa May walks past during a working dinner meeting at the NATO headquarters in May, 2017. Credit:AP Concerns about Trump and the reliability of the US security umbrella have spurred a series of discussions among European leaders about how to respond. The European Union has bolstered its own security cooperation, creating an embryonic fallback if NATO fails, for instance. And even if Trump holds back his signature from the NATO summit's final declaration - an unprecedented move for a US leader - diplomats who have pondered the possibility believe many of its most important initiatives would roll forward anyway, since they were already approved by defence ministers in recent months. Despite the fears about NATO's future, most countries are still spending far too little on defence to be self-sufficient if they were stripped of US protection. The biggest culprit is Germany, Europe's richest nation and Trump's favourite target for anger. Although Chancellor Angela Merkel has pledged to spend more on defence, the effort remains unpopular among German voters. Current plans would only bring spending up to three-quarters of where she pledged to NATO leaders it would be by 2024. Germany's soldiers have had to use broomsticks to train because they don't have enough guns. One European policymaker said that many leaders initially hoped to ride out a single Trump term, but they fear that he could be re-elected, giving him enough time to make many of his policy shifts permanent.

"It really does look like we're on the cusp of a new era, and we're not quite ready for that in the EU," the policymaker said. The talk of a NATO crack-up is so bad that even NATO Secretary General Jens Stoltenberg, who has typically tried to play down transatlantic disagreements, acknowledged the fears last month, shortly after the G7 summit. "It is not written in stone that the transatlantic bond will survive forever. But I believe we will preserve it," Stoltenberg said. "The lesson of history is that we have been able to overcome our differences." Some diplomats say they are puzzled by the gap between Trump's ire and the opportunity for an easy political victory at the NATO summit. Fellow NATO leaders, spooked by Trump, are expected to increase defence spending by 3.8 per cent this year, extending a trend that started under President Barack Obama. When Trump took office, only four NATO nations met the guideline of spending at least 2 per cent of their annual economic output on defence. This year, eight are on track to do so, with another seven set to get there by 2024. Ahead of the summit, NATO countries have also signed on to US security priorities on counter-terrorism and military readiness. Trump additionally has poured money into US military activity in Europe, asking for $US6.5 billion for the 2019 budget, nearly double the amount in Obama's final year in office.