Less than a week after complaining about Canada’s negotiating stance and appearing to despair of agreement, Donald Trump has hailed a new US-Mexico-Canada trade treaty in typically hyperbolic terms. It was, he said, “truly historic”; “the biggest trade deal in United States history”; “the most important” ever agreed by the United States.

The agreement, which needs to be approved by the US Congress and the legislatures of the other two countries, will replace the North American Free Trade Agreement (Nafta) finalised during Bill Clinton’s presidency, and appears to go some way towards addressing US concerns about cheaper Mexican labour taking jobs from the US. The US has also won concessions from Canada on exports of dairy products.

But opinion is already divided about the scale of the achievement: is it largely a change of nomenclature (the new treaty is set to be called the USMCA) and mere tinkering with Nafta, or does it address the concerns of Trump and affected US workers? According to Trump, “It’s not Nafta redone, it’s a brand new deal”, but the real answer to that question will probably emerge only with time.

What is worth noting more immediately is the rollercoaster course of the Trump administration’s approach. Only four days before agreement was reached, the US president had referred to Canada’s chief negotiator and foreign minister, Chrystia Freeland, in highly undiplomatic terms, saying: “We don’t like their representative very much” and the following day that “she hates America”. Once the deal was done, however, it was all sweetness and light. Trump sent Canadian leaders his “highest regards” and had nothing but compliments for Canada’s approach and the way Prime Minister Justin Trudeau defended his country’s national interest. At the same time, he insisted that without threatening swingeing trade tariffs, no progress would have been made.

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In other words, it was the same old Trump: the same Trump who had threatened fire and fury against North Korea and its nuclear missile tests and mocked the North Korean leader, Kim Jong-un, as “little rocket man”, before disregarding all the warnings to hold a summit meeting with him, and who now describes how Kim “wrote me beautiful letters and we fell in love”.

The question now is whether something of the same technique will work with the EU (on tariffs), with Iran (on sanctions and its nuclear programme), or even with China (tariffs and its growing military power).

On the EU, Trump has said that a “successful negotiation” was in progress – after Jean-Claude Juncker, the president of the European Commission, made a flying visit to see him and the EU retaliated with threats of tariffs of its own. At the same time, the US president has attacked the EU approach as “killing us”. And he made hay with Juncker’s accent at a recent “Make America Great Again” rally for the benefit of his domestic constituency.

Trump has stuck to his campaign pledge to withdraw from the international nuclear agreement with Iran, and the threat supposedly posed by Iran was at the centre of Trump’s bombastic address to the UN General Assembly last week. Now, though, with the Europeans trying hard to keep the agreement intact and devising ways of circumventing US sanctions, there are hints that Iran might be ready to talk about adjustments.

China, for its part, is so far giving as good as it is getting on the question of US tariffs, at least in the rhetoric department.

All of which could prompt two tentative conclusions. First, is it perhaps time for the rest of the world (and especially the western world) to stop panicking about Trump’s verbal excesses and regard them instead as part of his negotiating technique; as something of an opening bid, if you like. This may not be how the rest of the developed world, at least, likes to do diplomacy. This sort of exaggerated threat, followed by cajoling, followed by more threats, followed by an almost instant about-turn, it could be argued, is precisely what diplomacy has evolved to try to avoid. But hey, as Trump himself might say – and this might be the second conclusion – the approach can be effective. There are times when it has worked.

Now there are obvious risks here. The brinkmanship associated with Trump’s North Korean diplomacy appeared to place regional, if not global, security on a knife-edge until a very late stage. US policy – as distinct from Trump’s rhetoric – on Iran looks to be divided, with hawks led by John Bolton, Trump’s national security adviser, seeming to favour real, as opposed to rhetorical or tactical, belligerence. And Iran is no slouch when it comes to undiplomatic language either. It is also at the heart of one of the world’s currently least stable regions.

China is a whole other proposition, because of its size, its economic clout and the way it has started to extend the affirmative exercise especially of naval power. Then again, Beijing is probably not ready to take on the United States, either economically or militarily – if that is ever what it decides to do – and it may indeed be amenable to a deal on trade tariffs eventually, if terms can be hammered out. The world of the bazaar is something that China, like Iran, is familiar with. They may just not expect to face an American administration as practised at the same game.

The early verdict on Trump’s oft-derided diplomacy must be that it reflects the “realist”, transactional approach, taken to its ultimate degree, with all the minuses (the risks) but also the pluses (results: “deals”) that come with it. Nor should anyone really be surprised. This is no less than Trump held out during his campaign.

It might also be regretted (though probably not in Washington) that Congress has so constrained this president’s room for manoeuvre vis-a-vis Moscow that he has been unable to try the same approach with Russia, where it could potentially have had a beneficial effect. Both Trump and President Vladimir Putin seem to sense that a “deal” is there for the making – which would explain why they have generally refrained from personal invective. But, as the Washington establishment’s horrified response to the Helsinki summit showed, Trump is not in a position even to make his opening bid – and may well not be for the rest of term.

For those who find the Trump rhetoric too crude and – more crucially – too fraught with geopolitical risks, one consolation might be the effect that his administration’s approach is having on the European Union. Not only has it driven the EU into almost unprecedented unity, both on the matter of trade tariffs and on Iran, but it has encouraged the Europeans to use the real economic clout they have and to look for imaginative solutions – to continue trading with Iran, for instance, despite US sanctions – that they would not have considered before. Europe has some way to go on developing its defence and security provision, but there has been progress on that front, too.

At the same time, the international climate has changed. Donald Trump’s hyper-realism is having an impact on the way diplomacy is done and – like it or not – producing results.