What is the Brexit deal - and why is Arlene Foster so opposed to it?
Q. What was the deal on the table?
A. The UK had agreed with the EU's Brexit Taskforce that there would be "regulatory alignment" between Northern Ireland and the Republic after Brexit. This was essentially what the Irish Government had sought in a bid to retain the status quo regardless of what sort of trade deal is negotiated later in the process.
Q. What does regulatory alignment even mean?
A. It's a technical term that means a more flexible adherence to trade rules on either side of the Border. In practice, it could mean a whole raft of minute and technical rules - agreeing things like "what is cheese?" - could just continue.
Q. So why wouldn't the DUP support that?
A. As hard-line unionists, the DUP are concerned that linking regulations in Belfast and Dublin amounts to the creation of an all-island economic zone. They believe that Northern Ireland is part of the United Kingdom and therefore must leave the EU on exactly the same terms as the rest of the union.
Q. But surely Theresa May briefed the DUP before putting this deal on the table?
A. That's what everybody in the EU and Irish Government assumed. However at lunchtime yesterday, the DUP leader Arlene Foster rang Mrs May to outline her concerns.
Under normal circumstances, the British prime minister would have been in a position to tell them to live with it - but since calling a snap election last summer, Mrs May's minority government is propped up by the DUP's 10 MPs.
Q. Does that mean Brexit talks won't move to the next phase?
A. It certainly makes progression much harder, but there is time to reach a resolution.
While yesterday was seen as a major "stage post" on the way to Phase II, Ireland never viewed it as a "drop dead deadline".
EU leaders will gather in Brussels on December 14 and 15. That's when real decisions have to be made.
Q. Will Dublin offer up any concessions to try get the DUP on board?
A. No, Dublin and the remaining EU Member States believe it is the job of Theresa May to talk to the DUP.
Taoiseach Leo Varadkar has not spoken to Arlene Foster in recent days and at present has no plans to. Sources said the problem lies with the UK's handling of the talks.
Q. How can Theresa May convince Arlene Foster to take the deal?
A. It won't be easy. The DUP has already secured a multi-billion pound investment package for Northern Ireland on the back of their 'confidence and supply' arrangement with Mrs May. It's unlikely more money will be enough to get them over the line on this issue though.
Q. Could this collapse the UK government then?
A. No such threat has been made as of yet but Mrs May is in a very precarious place. If her government were to collapse it would almost certainly derail the Brexit talks.