Europeans ready for a lecture on defence spending, but the worry is Trump may go further

European leaders heading for a Nato summit in Brussels are not sure which Donald Trump they will have to deal with – the one who could throw a few temper tantrums but leave the transatlantic organisation intact, or the one who could provoke the biggest crisis in Nato’s 69-year history.

They are nervously bracing themselves for the worst. The leaders are ready for the US president to lecture them for failing to increase defence spending, but the worry is that he may go further. He could express his displeasure by cancelling US participation in one or more Nato exercises or by delaying the deployment of more troops and equipment to Europe.

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He could, without any prior consultation with Nato allies, strike a deal with Vladimir Putin when he meets the Russian president in Helsinki next week.

But even those who are most fearful believe Nato, the most powerful military coalition in the world, will survive. They argue that the next few days could be stormy but the organisation is too important to fall apart. The US military values Nato and would resist any move by Trump to walk away. And even in the unlikely event that Trump wanted to take the US out, it would not be that easy.

Douglas Lute, who served under Barack Obama as US ambassador to Nato from 2013 to last year, played down the prospect of a US withdrawal.

“Most of the policy decisions taken by President Trump in the first 18 months of his administration have been executive decisions. That means he holds, as the chief executive in our system, the power to do that, literally with the stroke of a pen,” Lute said.

“Nato is different. Nato is a treaty obligation which was taken by the nation of the United States. It was ratified by a two-thirds majority, which is required by our constitution, by the senate of the United States. And any structural change to that arrangement would have to go through the same process. So this is not something where any president – President Trump or any president – can simply sign America away from a treaty obligation. That would require an act of Congress.”

During the election campaign Trump described Nato as “obsolete”, and a constant refrain – repeated last week – is that the US is having to contribute too great a share of funds for the 29-member coalition. He argues that the US is basically subsidising European countries that would rather spend more on welfare than defence.

The US has been and continues to be the dominant force in Nato since the organisation’s founding in 1949 – the biggest contributor by far in terms of cash, personnel and equipment. Based on Nato figures for 2017, the US spends 3.58% of GDP on defence.

European members are well behind, with only five meeting a Nato target of 2% of GDP set at a summit in Wales in 2014. Greece spends 2.32%, the UK 2.14% and Estonia the same, Romania 2.02% and Poland 2.01%. France comes in at 1.79%, Germany 1.22%, Italy 1.13% and Spain 0.92%.

Looking at the figures as a share of GDP does not necessarily provide an accurate picture of contributions to military capability, and it can be hard to make a direct comparison. But the US is unquestionably the biggest beast in Nato and the UK and France the major military forces in Europe.

A European Nato diplomat said the best approach to Trump for the Europeans was to try to show they are listening to his arguments about increasing defence spending. “The aim is to pamper him more than Putin does,” the diplomat said.

The Nato secretary general, Jens Stoltenberg, will stress that two more countries – thought to be Lithuania and Latvia – have reached the 2% target this year and others are increasing defence spending. A further seven have promised to meet the 2% target in the next six or seven years.

In April, Emmanuel Macron promised France would increase defence spending by about a third to take it to the 2% target by 2025. Germany will be a target for Trump’s derision, planning only a modest increase.

When Trump described Nato as obsolete, it was an overstatement. But Nato does need reform and to work out what its role in the world should be. Founded as a counter to the Soviet Union, it has floundered since the fall of the Berlin Wall in 1989. It was slow to intervene in the Balkans but did so eventually, culminating in the bombing of Serbia in 1999.

Four years later, Nato invoked for the first time article five – which means an attack on one member will be met with a collective response by all – on behalf of the US after the 9/11 attack. Nato intervened for the first time outside Europe, taking command of the international force in Afghanistan.

The Russian annexation of Crimea from Ukraine in 2014 came almost as a relief to Nato commanders, who mistakenly believed they were returning to ground they were familiar with – the cold war, and a country with nuclear and conventional forces. But Putin has repeatedly wrongfooted them by engaging in hybrid warfare, an unexpected mix of deniable operations, disinformation and cyber-attacks.

Nato has been slow to react but on the agenda for the summit are a series of proposals for countering such hybrid warfare, such as beefing up its cyber-offensive capabilities and propaganda machine. It will continue to deploy battlegroups to the Baltic states. Although Nato has largely pulled combat troops out of Afghanistan, it will extend funding and troop deployment to the country – there are 16,000 there at present – to help train Afghan forces. The summit will also agree a new training mission to Iraq.

Nato has continued to expand, with the Republic of North Macedonia set to join. The Kremlin will not be relaxed about the prospect of Georgia, on Russia’s southern flank, becoming a member. Nato, anxious to avoid another flashpoint, is far from ready to agree to Georgian accession but it will give the country an acknowledgement of the progress it is making.

Trump could justify a move away from Nato as a strategic shift away from Europe to the Pacific. The US administration, and most European governments apart from those in the Baltic states and others bordering Russia, view Russia as a declining power, incapable on an invasion eastwards. The US sees China as a power on the rise, a potentially formidable economic rival, with lots of potential flashpoints in the South China Sea and elsewhere.

But Nato is still central to US military strategy, not only in Europe but for its potential to intervene elsewhere around the world, as it has in Afghanistan.

The Australian former prime minister John Howard, one of America’s staunchest supporters during his premiership, shares that assessment. In response to a Guardian question at the Policy Exchange thinktank in London, Howard said: “Everyone can try and anticipate what President Trump is going to do. I don’t think he is going to walk away from Nato. I think that is a ludicrous proposition.”

A former Nato secretary general, George Robertson, agrees. He has watched other US presidents – Bill Clinton and George W Bush – come into power, like Trump, sceptical about Nato, only to eventually recognise its value.

“You can have plenty of ad hoc coalitions, coalitions of the willing, but nothing beats the permanent coalition that happens to be the Nato alliance,” Lord Robertson said.