The relationship between the DUP and the British government has been showing signs of crumbling in recent weeks but it is now clear that trust is breaking down as we edge closer to a Brexit deal.
Senior DUP figures spoke out in angry terms yesterday following the leaking of a letter from Theresa May in reply to an earlier message from Arlene Foster and Nigel Dodds.
Mrs Foster said the prime minister appeared 'wedded to the idea of a border down the Irish Sea', despite Mrs May regularly insisting that is not what she wants.
In the letter, obtained by The Times, the prime minister says the EU wants to maintain a Northern Ireland-only 'backstop to the backstop' in case future negotiations are unsuccessful.
She said: ''I am clear that I could not accept there being any circumstances or conditions in which that 'backstop to the backstop', which would break up the UK customs territory, could come into force.''
But she acknowledged that the 'unique circumstances' of Northern Ireland 'could require specific alignment solutions in some scenarios' on regulations.
Sammy Wilson said the letter's wording means the government 'has accepted there will be a Northern Ireland-only backstop, that that backstop will require specific alignment for regulations'.
He referred to a 'breach of promise' while Mrs Foster said the letter 'raises alarm bells for those who value the integrity of our precious union'.
Where all this leaves the confidence and supply arrangement is not entirely clear but there is no doubt we are a long way from the broad smiles and warm handshakes in Downing Street that sealed the deal and helped keep Mrs May in power.
It is not just the DUP that is causing Mrs May difficulties.
Yesterday she faced a new headache with the resignation of transport minister Jo Johnson.
Unlike his better known brother, Boris, Jo Johnson was a Remainer and says the withdrawal agreement which is being finalised in Brussels and Whitehall will be a 'terrible mistake.'
He has added his voice to those calling for a second referendum, saying the reality of Brexit has turned out to be far removed from what was promised.
He is not alone in thinking that way although it could be argued it was far from clear even in June 2016 exactly what was being promised.
Many of those promoting a Leave vote did not fully think through the consequences of exiting the European Union.
The DUP enthusiastically supported Brexit, despite warnings at the time that it could herald the break-up of the union.
And here we are, two years on, and the party is desperately fighting to maintain the 'integrity of our precious union'.
