Any hope that the European Union’s position in full solidarity with Ireland over the backstop would recede as Brexit got closer is more or less now extinct.
Dublin’s interpretation of the backstop is clear: that there can be no divergence between Northern Ireland and the Republic in terms of customs or regulations, ever. That is what it is trying to tie down legally.
Such a concession might in practice have minor consequences in the early years of Brexit, while the UK kept most of the same regulations as the EU, which have converged over decades. The problem is the principle: Northern Ireland would forever be on the EU-Irish side of the regulations divide, no matter how much they diverged in future. Ireland, let alone republicans, would never allow a return.
This must not happen or the DUP will have little option but to end the confidence and supply agreement.
Indeed, it is alarming that the government is on the verge of agreeing it. One of the reasons that this has been able to happen is that the government always said it disagreed with the EU interpretation of the backstop, which Britain seems to have considered to be a fudge to move things to the next stage.
But in much the same way that Theresa May had not prior to the Chequers proposals in July fully revealed her intentions for a much softer Brexit than her rhetoric had previously, it has not until recent weeks become clear that the UK resistance to the backstop is minimal.
In fairness to Mrs May, she has been clear that there will be no customs border in the Irish Sea. In fact, she is proposing to keep the whole of the UK in that union to prevent such an internal border.
But the regulations alignment plan for Northern Ireland would have huge ramifications and be confirmation to Dublin that the UK has conceded that there can never be any customs or regulatory divergence at the land border, but can be at the Irish Sea — a massive and disastrous concession.