Instead diplomats and officials say the volatile billionaire appears to be firing his opening salvo in a new push to pressure Washington's allies to do more.

"It's obviously completely unrealistic to imagine virtually all NATO allies coming to the five percent level, at least in the near term," said Ian Lesser of the German Marshall Fund think tank.

"It's part of what will be the very tough diplomacy around defence burden-sharing with the incoming Trump administration."

- Where are we now? -

After Russia's invasion of Ukraine, NATO countries stepped up spending and in 2023 turned their decade-old goal of two percent of GDP into a baseline requirement.

Last year 23 of NATO's 32 member countries were on course to hit that threshold -- with Poland leading the pack on 4.12 percent.

Leading military power the United States is on 3.38 percent, while Britain spends 2.3 percent and France and Germany have just crept over the two-percent line.

Spain is the worst in class on just 1.28 percent, failing to meet the bar along with the other laggards including Italy, Canada, and Belgium.

Given the relative size of its economy, US defence spending in dollar terms accounts for over 60 percent of NATO's total.

- How Trump sees it -

Trump has long been sceptical of the role the United States plays in underpinning Europe's security in NATO, accusing allies of free-loading on Washington's largesse.

During his first term he berated the likes of Germany for underspending and reportedly had to be pulled back by fellow leaders from following through on a threat to quit the alliance.

On the campaign trail this time round he called the current NATO baseline "the steal of the century" and said he'd encourage Russia to go after countries not spending enough.

"They can all afford it, but they should be at five percent not two percent," Trump said Tuesday.

"Europe is in for a tiny fraction of the money that we're in."

- Others agree (sort of) -

Trump is not alone in demanding that NATO's defence spending rise.

The alliance's Secretary General Mark Rutte has stated clearly that two percent is not enough given the scale of the threat posed principally by Russia.

He insists Europe needs to "turbocharge" its spending to fulfil new defence plans and deter Moscow from launching a future attack against NATO territory.

Rutte has not offered a new target figure -- but he said if NATO members do not spend more efficiently together then they could have to "to go to at least four percent".

That urgency is echoed by countries close to Russia such as Poland and the Baltic states which have already been pushing for a higher target.

And even allies that remain under two percent admit that spending will have to rise.

But Trump's five percent figure is "total madness" said German lawmaker Ralf Stegner, from chancellor Olaf Scholz's Social Democrats.

- What happens next? -

NATO diplomats say that however unrealistic Trump's demand may be -- the alliance will need to meet him part of the way at least to keep him onboard.

"If Trump is calling for five percent than we have to find a solution that works for everyone," one diplomat told AFP on condition of anonymity.

The first step will be seeing how the notoriously mercurial Trump's comments transform into policy once he's inaugurated.

Then there will be haggling to try to forge a new consensus figure by NATO's June summit in the Netherlands.

"They'll need to say that we must move towards three, 3.5 percent," said Camille Grand, of the European Council on Foreign Relations.

"Last time with two percent we gave ourselves 10 years, now perhaps we should look to do this in five."