They had barely touched the breakfast orange juice before the verbal brawling began.

In the Nato corner defending the alliance was General Secretary Jens Stoltenberg while in the US corner out to teach the Nato chief a lesson was US President Donald Trump.

It was Mr Trump though that came out swinging, weighing in with claims that Germany is a “captive” and is “totally controlled” by Russia because it made a “massive oil and gas deal,” with Moscow.

Calling some Nato members “delinquent,” because “the United States has had to pay for them,” Mr Trump’s confrontational start to the Nato summit at a breakfast meeting in Brussels yesterday was blistering if not entirely unexpected. The US leader has often expressed his frustration that some Nato members are not paying their way.

For his part Mr Stoltenberg did his best to dodge the verbal punches, countering with more considered language that, “despite differences,” Nato was about uniting “to protect and defend each other.”

Later though German Chancellor Angela Merkel was far less accepting of Mr Trump’s all out attack. She made it clear that few knew better then her what it meant to be a “captive” nation. To that end the Chancellor offered a reminder of learning first hand what it means to be a ‘captive nation’ after growing up in former Communist East Germany. Modern Germany, she said, is not that.

So there it was, the opening rounds of a Nato summit most anticipated would be acrimonious but surely could not have foreseen as being as fiery from the outset.

To put this in context let’s remember that these are supposed Nato ‘allies’ talking and that the Brussels summit comes less than a week before Mr Trump is due to hold his first summit with Vladimir Putin, in Helsinki, reviving concerns among US allies over his proximity to the Russian president.

For his part Mr Trump has something of a point both in highlighting Germany’s vulnerability through dependence on the Russia - Germany gas pipeline and on the shortcomings of some Nato members when it comes to paying their way within the organisation.

That said there are those who might argue that Mr Trump’s ‘outrage’ at the pipeline might also have been raised to deflect accusations that he himself has been too cosy with the Russian president, charges bolstered by the continuing investigation into Russian interference on his behalf in the 2016 election.

For some time now Mr Trump has done his best to dismiss former FBI director Robert Mueller’s investigation as a “witch hunt,” into whether the Trump presidential campaign colluded with Moscow to help him into the White House. The US president who has never been shy on lavishing praise on Mr Putin has always vehemently denied unsubstantiated allegations that Moscow has compromising material on him.

Given all of this, as well as yesterday’s bad tempered start to the Nato summit and Mr Trump’s impending one with Mr Putin, questions are again being raised as to the real nature of the relationship between the two leaders. Just what is the extent of the perceived affinity between the two men? Most significantly what potential if any does it have right now for undermining Nato if Mr Trump decides to seek a ‘reset’ of relation with Moscow?

“We don’t know what’s in that box,” a former US administration official was quoted by the Financial Times as saying this week, referring to the Trump-Putin relationship. “There might be nothing in that box. But the box is still there.”

It’s precisely the fact that it’s still there that has so many leaders of Nato countries currently very nervous. The main concern remains not whether Trump and Putin will get along or not in Helsinki, but on what basis?

Agreements between these two powers are not just a matter of self interest but whether the outcome of such agreements are also in the world’s best interest. Myriad contentious issues many of them already flashpoint are shaped or could be shaped by what Mr Trump and Mr Putin agree or disagree on. Syria and Iran are but two of the more obvious.

There remains other frictions and dangers too. Russia’s interference in US domestic affairs, illegal annexation of Crimea in Ukraine, intimidation of Nato members, and violation of numerous nuclear and other arms control agreements, all remain open points of conflict.

Right now the United States and Russia retain the world’s two largest nuclear arsenals, and both are engaged in massive modernisation programmes to enhance the military utility and longevity of their forces.

To imagine such things being the topic of discussion let alone deals being done by Mr Trump outwith Nato’s approval and consensus is for many in the alliance the stuff of nightmares. Mr Stoltenberg and others in Nato know all too well that the risk of US president might giving Russia multiple concessions on Nato, sanctions, Ukraine, or elsewhere is all too real.

Which brings us back to the intriguing issue of relations between these two men. Whatever the level of admiration and respect Mr Trump appears to have for Mr Putin he cannot expect to turn up in Helsinki and simply wing it, as so often appears to have been his approach in the past.

For his part Mr Putin will come to the summit very well prepared to push his agenda with a gullible American counterpart.

If one thing was clear from yesterday’s face off between Mr Trump and Mr Stoltenberg it’s that

such transparent divisions with Nato’s ranks only weaken Mr Trump’s position in Helsinki. Yesterday’s verbal boxing in Brussels simply plays directly into what western intelligence agencies and foreign powers assess as Mr Putin’s ultimate goal, to cement his own autocratic rule by weakening the institutions of the West.

The real fears of Nato members in Brussels were summed up yesterday by Thomas Kleine-Brockhoff, a former German presidential adviser who was attending the summit.

“The question everybody has here is what is the world going to look like after this couple of days here? Is an already undermined system getting a further blow?”

Perhaps the real and most definitive answer to that lies not in Brussels but in Helsinki in the coming days.