Normally it is difficult for a visitor to arrive in Ireland without seeing large signs proclaiming how welcome they are. The fusillade of unionist hostility that marked Joe Biden’s visit to Belfast suggests a very different message. You would almost think that everything in Northern Ireland would have been sweetness and light if only the US president had had the decency to have stayed away. Unionist politics deployed big guns against Biden’s visit. The former Democratic Unionist party leader Arlene Foster can be quite pragmatic; on Wednesday, even she declared that he “hates the United Kingdom”. Her former deputy, Nigel Dodds, dismissed the president as “transparently pro-nationalist”. Predictably, the DUP MP for East Antrim, Sammy Wilson, suggested an even darker purpose, charging Biden not just with the crimes of being “anti-British” and “pro-republican” but of “trying to force the UK to fit into the EU mould”. It would be easy to dismiss these attacks, and to treat them simply as the cries of wounded unionists whose one-time hegemony within Northern Ireland politics has been diminishing. That historical shift in unionist fortunes is certainly a factor here. The attacks on Biden should, though, be taken seriously in their own right. They speak to the lack of trust that still permeates Northern Ireland politics, a quarter of a century after the Good Friday agreement ended 30 years of the Troubles. One immediate explanation for the ferocity of the language against Biden is that on 18 May the DUP’s electoral credibility is on the line in Northern Ireland’s local elections. On the one hand, the party is desperate not to bow to pressure to resume power-sharing and find itself “out-unionisted” at the polls by groups such as Traditional Unionist Voice. On the other, it is looking for big wins and strong turnouts in unionist areas that will strengthen its campaign against Rishi Sunak’s remodelled post-Brexit plans and enable the party to re-enter power-sharing from a position of increased strength. Biden’s visit has provided a big platform for an election that will have significant consequences. No one expects that power-sharing will be on the agenda until after these elections. But a second explanation for the hostility is the ambiguous and anachronistic narrative about Irishness in which this president wraps himself, and which he has now taken on to the Irish Republic. Biden’s self-identification as an Irish American leader is central to his politics. His Irish ancestry is a fact. So, as it happens, is his English ancestry (he hails from Sussex), to which, very unusually and surely on diplomatic advice, he referred when he spoke on Wednesday at Ulster University in Belfast. But it is the Irishness with which he identifies, not the Englishness, and his particular version of Irishness is freighted with histories and cultures that are weakening in the 21st century. Hostility to the British and the English – the main charge from the DUP – is part of this. In fact, in Ireland itself, though you should not oversimplify, anti-British feeling is diminishing, or was until Brexit. Even so it’s only a part of something larger. As Fintan O’Toole argued this week, Biden comes from a family-priest-school Irish American experience that still exerts idealistic sway in the US, but from which modern Ireland has decisively moved away, not least because of child abuse scandals. That old Catholic Irishness was actually one of the causes of the 20th-century conflict, the anniversary of whose pragmatic end Biden is in Ireland to mark. At some level, Biden surely understands that Catholic Ireland has been irrevocably changing during his lifetime. In a similar way, he surely also sees that a Britain with a Hindu prime minister is not exactly the same as the Britain of the Famine or of the Black and Tans. Yes, Biden’s Aunt Gertie once told him: “Your father is not a bad man. He’s just English.” And, yes, Biden famously (at least in this country) brushed the BBC aside on the campaign trail in 2020 by saying he didn’t need to speak to it because he was Irish. But the DUP draws historically inflexible conclusions from such anecdotes. The public Biden is, above all other things, a highly experienced politician. He has spent his whole career trying to negotiate deals to get legislation enacted as pragmatically as possible with opponents. He is pretty good at it. He is undoubtedly easy to underestimate, partly because of his age and partly because of a speaking style that is shaped by his determination to overcome his stammer. But a lifetime on Capitol Hill and the White House means he is well equipped, not badly equipped, to understand the subtleties and anxieties of Northern Ireland. His conversational speech in Belfast showed this. It was certainly not a speech for the ages. But it read the uncertainty of the room correctly. It was essentially optimistic, and it cast the US as the enabler of progress. But it said absolutely nothing about Irish nationalism or unification. There was no partisanship in it at all. It showed that Biden – and his speechwriter – gets the big picture and the subtleties of Northern Ireland a lot better than the critics claim. This week’s attempt by the DUP to cast Biden as an interfering Irish nationalist is simply false. It helps no one to pretend this. There is no doubt that Washington and London would have preferred the 25th anniversary of power-sharing to have been more full throated. But the fault for that does not lie with the man in the White House. It lies with those who created the post-Brexit logjam of the peace process but who have absolutely no strategy at all for ending it. Martin Kettle is a Guardian columnist Join our panel of speakers including Jonathan Freedland, Mark Durkan, Lorn Empey and Monica McWilliams as they mark the 25th anniversary of the Good Friday agreement and look to the future of Northern Ireland. On Monday 24 April, 8pm–9.15pm BST. Book tickets at theguardian.com/guardianlive