John Key had a good and easy relationship with President Obama. They may have come from different positions on the political spectrum, but they shared similar values and seemed to like each other.
Our Prime Minister's relationship with President Trump may not, though, be so easy. There are so many aspects of the new President which are problematic. And John Key will not be the only leader across the globe who will be unsure, at this point, quite what to expect.
There will be many foreign capitals trying to assess whether the Donald Trump they saw as a campaigner for the presidency is the same man as will take up residence in the White House. They will be asking themselves how they should respond to a man who seems to fly in the face of so much of what they might normally expect from an American president.
Are they to take seriously his proposal to build a wall on the Mexican border? And what about his promise to deport millions of supposedly illegal immigrants? Even more seriously, has he really committed to re-introducing torture, including waterboarding, as a counter-terrorism weapon? How many of America's usual allies would willingly align themselves with a publicly declared policy of that kind?
And what are they to make of a President who takes such a cavalier attitude to the constitutional proprieties? Who seems so keen to use his position to enhance his personal business opportunities? Who is so clear in his intention to abolish Obamacare so that poor families are left without access to medical care - and to stack the Supreme Court with his own nominees in order to roll back the policy advances on social policy issues that have been made over recent years? Whose initial appointments include those whose records are sullied by racist attitudes - appointments that have been welcomed by extremist bodies?
Is he to be believed when he promises to impose tariffs on imports from trading partners and to introduce a comprehensive range of protectionist measures? Will he really make good on his promise to scupper the TPPA - a proposal that will be welcome to many, myself included, but that will alarm many others, including John Key.
And what about climate change? Will he really water down the consensus, arrived at after so much effort, on the need for action? And what would that mean for small Pacific nations in particular?
Above all, will a Trump-led America be a reliable ally? Will it stand by its friends if they are threatened by hostile forces? Or does "put America first" mean a withdrawal into isolationism?
Some Trump allies can be heard to say that the stances he has taken on these issues should not be taken too seriously - but in that case, why did he commit to them? If they were merely commitments made for the purposes of the election campaign and can therefore be disregarded, what does that tell us about the reliability of anything that President Trump might say in the future?
Underpinning many of these concerns is perhaps a deeper anxiety. President Obama's dignity, good sense and wide understanding of the world epitomised what many expect from someone who is inevitably and by default recognised as the leader of the free or democratic world. But when we recall the Trump we have come to know - the bigot, the braggart, the self-obsessed chancer, the groper of women, the purveyor of insults - do we see someone who has the moral and intellectual standing to lead us? Does he represent an exemplar of the great virtues of democracy and a symbol of hope to those millions who are denied its advantages? Can he earn the respect that his job demands?
Little wonder, then, that a Trump presidency is viewed with some concern by leaders around the world. That world is now a different place, for good or ill.
John Key, and others similarly placed, must make the best of it. They have no option but to deal constructively, so far as they can, with the new leader of the world's most powerful country - but, in the course of doing so, they might see the need to let him know just what is now required of him by his new responsibilities.
- Bryan Gould is a former British MP and Waikato University Vice-Chancellor