What the party decides to do will not only have a profound effect upon the reputation of the DUP, but could be crucial to the very existence of Northern Ireland.
But to guess where things might go in the future, we need to go back to the very start.
Many people remain baffled as to why the DUP ever wanted to leave the EU. By 2016 Northern Ireland had become constitutionally stable, with record support for the Union. Since the vote to leave, the shock of the decision itself and the shambolically destabilising nature of the Brexit negotiations which then unfolded have eroded that support.
Some nationalists believe that hardline DUP figures had a calculated strategy to leave the EU in order to see a hard border and thus differentiate Northern Ireland from the rest of the island. In truth that is unlikely to have featured much in their thinking – and almost certainly not in the thinking of the leadership.
Linfield v Portadown Sunday clash: Breakers of the Sabbath will answer to God
Thousands expected to take part in 'Derry Day' this weekend
Esmond Birnie: The protocol is not as claimed boosting growth in Northern Ireland
NI Weather: 45 pictures of how we enjoyed wall-to-wall sunshine
Crawfordsburn Country Park: Five PSNI officers injured bringing crowd of 600 under control - two teens arrested - parents asked to know where their children are
From its formation in 1971, the DUP preached hard line Euroscepticism. Founder Ian Paisley’s fusion of fundamentalist Protestantism with politics led to him presenting the EU as a “satanic” force. As late as 1998, he was describing the EU as “a beast ridden by the harlot Catholic church, conspiring to create a Europe controlled by the Vatican”.
While many DUP members would give little credence to that proposition, they were instinctively anti-EU for more prosaic reasons, including the EU’s curtailment of British sovereignty.
Over time, the DUP came to pragmatically recognise that there were benefits to the EU. But even as the party modernised and expanded, it remained Eurosceptic.
Therefore, when it became clear that a referendum on EU membership was to be called, backing a remain vote was always impossible.
And yet, for some reason, the party prevaricated. Whereas for months Sinn Féin and the SDLP were stating that they would campaign to remain, the DUP waited to see what would become of David Cameron’s attempts to renegotiate the terms of EU membership.
But in that vacuum, senior MP Sammy Wilson began moves which made clear that regardless of what the party decided, he would be campaigning to leave. In November 2015, the former Stormont Finance Minister joined Ukip leader Nigel Farage at a Leave.EU event.
When Ukip challenged the DUP to “come off the fence”, the party denied that Mr Wilson was out of step with its policy. But it was clear that he was advocating a policy which the party said had not yet been decided.
In January 2016, Arlene Foster took over as DUP leader. When I asked her about the continued uncertainty over the party’s stance, she responded that the DUP would “definitely” back one side but would “wait and see” what the PM could negotiate before picking a side.
Later that month Mr Wilson emphasised that he would not be waiting. He attended a cross-party Grassroots Out meeting where he signed ‘The Kettering Declaration’, pledging to work to leave the EU.
Days later, the confusion led to DUP MEP Diane Dodds mocking Mr Cameron’s renegotiation, saying that he wasn’t asking for enough from the EU – but then refusing to say that the DUP would definitely campaign to leave.
In early February, Mr Wilson’s friend and fellow ardent Eurosceptic Ian Paisley Jr went on the Nolan Show and, when asked about the DUP’s EU referendum stance, he said confidently that within “hours... definitive positions will emerge”. That did not happen.
But the following day, Mr Wilson told the Commons that the EU reforms on offer amounted to a “dodgy deal which even Del Boy would be embarrassed to be associated with”.
Yet still the DUP would not say which way it would go. It would take another 15 days for the DUP to do so and it only did that at the last possible moment, on the day that the vote was called and in doing so the party said that the decision was taken “on balance”, with an implicit nod to the fact that not everyone would agree. While the best that the DUP’s small but senior band of pro-EU members could have hoped for was that the party would stay neutral, Mr Wilson’s actions preempted that decision and put pressure on Mrs Foster.
Recent academic research by Mary C Murphy and Jonathan Evershed of University College Cork sheds further light on what went on around that period. The report, part of a collaborative three-year ESRC project ‘Between Two Unions: The Constitutional Future of the Islands after Brexit’ involving UK and Irish academics, included private interviews with multiple DUP figures.
One DUP MLA told them: “I was at the policy-making conference that we had – I say conference, it was a meeting upstairs – where they said, ‘right gentlemen, we need to agree our policy on Brexit’ – this was before the referendum. And 10 minutes later we had agreed our policy. We just went round the room and it was, ‘Burn it! Shoot it! Strangle it!’”
The academics believe that “the DUP’s coming out for leave was as much a matter of party management and political expediency as of ideological principle” and that an unprepared leadership never expected to win. They quote a DUP MLA saying that they were “gobsmacked” when they won and that “obviously, we hadn’t developed policy on the basis of Brexit [but] now we’ve had plenty of time to develop policy. And that policy is out on the strongest possible terms!”
There are obvious differences between then and now. Unlike 2016, the DUP now understands the significance of this decision. Mrs Foster is also now much weaker than she was then, yet the DUP has the power to topple the government.
But there are unmistakable similarities. Just as it prevaricated then over its decision, now it is delaying stating what precisely it wants. Its “one red line” of no Irish Sea border leaves everything else, including the customs union and single market, being negotiable. The logic of that one red line is that the party could support either the softest of Brexits or the hardest of Brexits – no deal – because either keeps the UK intact.
Mr Wilson is again at the vanguard of the intra-DUP debate and appears to be discreetly pushing no deal if the backstop remains, writing in the News Letter this week that the UK can leave with no deal.
But this time he is not the only voice. Others are alive to the strategic importance of this move. Interviewed by Mark Carruthers on The View on Thursday night, DUP MP Gavin Robinson was asked whether the DUP could support a very soft Brexit. In response, he gave a “qualified yes”, saying that there would be “earnest engagement” on such a proposal if it protected the Union.
If the DUP backs a Brexit in name only, it is vulnerable to internal rows and to rivals asking why it argued for the nation to go through such vast upheaval for such a small change which will rule out many of the potential benefits of leaving the EU.
But no deal carries the risk that the cultural nationalists and growing non-tribal group of voters who will be critical to the Union’s survival could reassess their constitutional preference. Even if some of the claims about no deal are hyperbolic nonsense and even in a best case scenario where there are no significant economic or social disruptions, there is still a risk for unionism.
For both sides, Brexit has always been as much about emotion as about facts. If people feel that a disastrous decision has been taken, it could be very difficult to persuade them otherwise – and the DUP is supremely unsuited to persuading non-unionist voters of anything.
The academics conclude that “no party has been more impacted by Brexit than the DUP” with the issue fuelling its mistrust of nationalism, Dublin and Brussels while also having “reinforced suspicions about the extent to which the British government is a reliable guarantor of unionist interests”.
Publicly, the DUP will almost certainly continue to sound bullish. But privately, senior figures know that they are involved in momentous and uncertain decisions of historic significance.
l Ben Lowry, page 11