A DIY enthusiast drills through his hand while putting up a shelf. Who’s to blame? Is it the manufacturer of the shelf? Was the drill broken? Or is the man himself to blame for his shortcomings?

No, it’s the electricity company’s fault.

That’s basically how the inside of the DUP’s head works. Whatever political setbacks befall them, nothing is ever their responsibility. They are always sinned against. Betrayal is everywhere. Quislings abound. Syrupy self-pity is their default setting.

We were treated to another display on Saturday at their annual conference.

‘Bin the backstop’ proclaimed deputy leader Nigel Dodds.

‘It will require the collective will not just of this party but of all who value and cherish our precious union to stand firm in the face of the inevitable onslaught’ he said.

‘Onslaught?’ The ‘threat’ to the Union is because the EU’s border with the UK has to go somewhere and – commendably – Theresa May doesn’t want to undermine the Good Friday Agreement settlement by reconstituting a hard border. That’s it. No onslaught, or betrayal or sell out. The UK’s Brexit compromises were always going to take place on Irish soil. Everyone – certainly those of us watching from Britain – could see that.

Yet the DUP’s naiveté apparently stretches to misunderstanding that ‘our precious Union’ – Theresa May’s hoary circumlocution – is merely a politician’s line. At best it’s a qualified position. The UK is not an arrangement of equals. After all, 97% of our population lives in Britain. And no British Prime Minister is going to elevate the delicacies of unionists over the needs of British jobs. Treating Northern Ireland as a special case is in the British national interest. Always was, always will be.

The sort of compromise deal the Prime Minister has agreed was coming down the line from Day One. Why didn’t the DUP see that and prepare for it? They could have been arguing all along that special status gives Northern Ireland the best of both worlds and that being treated differently is merely a product of geography rather than a harbinger of Irish unity.

Instead, the DUP finds itself mired in a mess it helped to create, serving as the useful idiots of the Tory Brexiteers. They are never the architects of their own fate, the captains of their own souls. I’ve written here before that political parties evolve and modernise in part by repudiating their own pasts. Not the DUP. What need is there of self-reflection when you’re always right?

The DUP remains inherently unreasonable. Not just in its characteristic belligerence and tantrum-throwing. No, it’s wider than that; it cannot actually reason. Its thought processes are simply otherworldly, the product of existing for so long in a consequence-free environment. It doesn’t matter whether it’s casual sectarianism or believing in sky bridges to Scotland.

No, the DUP is sinking. It will be damaged by whatever Brexit scenario now plays out. If Theresa May’s withdrawal agreement scrapes through the Commons, either with or without the DUP’s backing, they lose. The backstop becomes a fact of life.

Alternatively, if they help to scupper the deal and the UK crashes out of the EU, the DUP also loses. Having dodged real scrutiny for so long, I’ve lost count of the number of Westminster insiders and journalists I speak to who have never paid much attention to Northern Ireland but are now seething about their malign role in British politics.

The centre-left – Labour, Lib Dems, Plaid and the SNP – will never forgive them for dumping us with a hard border, massive regulatory uncertainty, a likely recession and an inevitable public finance crisis in trying to deal with it all. Frankly, neither will One Nation Tories.

Not to mention the impact of ‘no deal’ will rip through the DUP’s core constituency. That’s why the Ulster Farmers’ Union and various business organisations were so clear last week they were in favour of Theresa May’s proposed withdrawal deal. They know that the €3 billion that comes to Northern Ireland each year in the shape of EU agricultural subsidies will never be replaced like for like by the British government.

They also realise – which the DUP appears not to – that with so many fires burning in the event of a DUP-facilitated no deal Brexit, Northern Ireland’s interests will be at the back of the queue.

Arlene Foster has driven Unionism into a political cul-de-sac from which it will emerge diminished and in retreat.

And it will all be the DUP’s own fault.