THE Democratic Unionist Party and the Conservatives have not always been firm friends. Back in the early 1980s, Reverend Ian Paisley, the unionist party’s founder, accused Margaret Thatcher of “lying through her teeth” over her dealings with the Irish government in Dublin.

When the then Tory leader signed the Anglo-Irish agreement in 1985, Paisley’s booming voice declared “never, never, never” to the deal to thousands outside Belfast city hall.

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More recently, however, the DUP has been the party that likes to say yes to Theresa May. The Prime Minister, too, has been at pains to accommodate the unionist MPs from across the Irish channel upon whose support her minority administration depends.

From the £1 billion in extra cash for Northern Ireland agreed as part of the “confidence and supply” deal last summer or May’s frequent warm words about protecting “the precious union”, the DUP has often been seen as very much carrying the whip hand in its dealings with the Tories.

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But no longer, it seems. This week, the honeymoon ended between the DUP and the Tories, and May in particular. Whether the romance can be rekindled is very uncertain.

As ever in British politics right now, the critical stumbling block is Brexit. While Northern Ireland voted to remain in the European Union in June 2016, the DUP campaigned for Leave. Arlene Foster’s party even took advantage of outdated Northern Irish donor secrecy laws to accept a £435,000 donation from a still secret source to fund their Brexit campaign.

Since the Brexit vote – and particularly since the 2017 General Election when May’s premiership became tied to a small, fundamentalist unionist party – the DUP’s “blood red line” has been that Northern Ireland must leave the EU on the same terms as the rest of the UK.

The party has remained implacably opposed to the so-called Irish backstop, which would see Northern Ireland remain in a customs union with Brussels even if no trade deal is secured by December 2020.

For many months, Theresa May maintained – at least publicly – the notion that customs checks at Larne and Belfast would fatally undermine the integrity of the United Kingdom. The union, she said, depended on everywhere in the UK being treated the same (except, of course, for gay marriage, abortion and, if the DUP had its way, corporation tax rates).

But, in reality, any accommodation with Brussels was always going to come with special provisions for Northern Ireland, and its 310-mile-long border. When that deal arrived, at the start of this week, the DUP response was so bellicose it harked back to Paisley’s rabblerousing days.

The National:

Ramping up the anti-Tory rhetoric: The DUP's Sammy Wilson

Sammy Wilson, the party’s Brexit spokesperson, compared May’s deal to a “punishment beating”.

Nigel Dodds declared that agreement with the EU would leave Northern Ireland “subject to the rules and laws set in Brussels with no democratic input or any say”.

The ferocity of the response from DUP MPs was indicative of how power has shifted within the party from what are seen as more moderate voices in Belfast to the more hardline Westminster contingent.

With the Stormont assembly in abeyance – and Arlene Foster effectively without a role – Dodds, a former Vote Leave board member, is seen by many as the DUP’s de facto leader.

Within hours of May’s declaration, civil servants in London were told to remove DUP contacts from planning emails which the Northern Irish party would previously have been looped into. Few commentators expect the DUP to back May’s deal, making its passage through Parliament even more uncertain.

May, however, appears to have already factored in DUP intransigence. Indeed, many of the Prime Minister’s closest aides and supporters have been longing for such a moment ever since Foster – and Dodds – publicly humiliated May at last December’s EU summit.

That December move – in which the DUP threatened to bring down May’s Government if she did not change the wording on the Irish backstop – was classic DUP. Lots of political capital spent with not much return.

IN contrast to the depictions of the party as Machiavellian geniuses that propound in the British press – canny Ulsterman who always hang on for the best price – the hardline unionists have often been great at tactics but woeful at strategy.

The botched renewable heating incentive scheme was a boon for many of the party’s rural voters but brought down Stormont, and could yet cost Foster her scalp.

Similarly, the party has, despite its power in Westminster, found itself on the wrong side of the Brexit argument in Northern Ireland.

Moderate unionist voices, who have implored the DUP to take a softer line, have often found themselves looking to Dublin for protection, a remarkable turnaround in all-island relations.

At the same time, Brexit has brought the border into play in Irish politics for the first time in generations. The prospect of checks near Newry and Enniskillen does not mean a united Ireland – or a return to large-scale violence – is just over the horizon but it has reawakened questions of identity and belonging that were, if not quite settled, at least undisturbed.

Banging the union drum – as the DUP has done loudly, lately with support from Scottish Conservatives – is often a vote winner. Foster’s party has never been more popular, winning a record 10 seats in last year’s General Election. But with Protestants already in a minority in Northern Ireland, the DUP’s extreme Brexit stance will only further alienate the phlegmatic middle ground upon which the union rests.

The DUP risks ostracising its traditional supporters too. In one of the most remarkable scenes in a week hardly free of drama, DUP MP Jeffrey Donaldson upbraided the Ulster Farmers Union after the farming body called on the Democratic Unionists to back May’s deal to avoid a “disastrous” no-deal Brexit.

The DUP is learning the same lesson Edward Carson did almost a century ago – Ulster unionists should be wary of Conservative pledges of unswerving support. “What a fool I was. I was only a puppet, and so was Ulster, and so was Ireland, in the political game that was to get the Conservative Party into power,” Northern Ireland’s founding father said in 1921.

Former Ulster Unionist party communications director Alex Kane cautioned the DUP to heed Carson’s words. “The megaphone and public threats will not sort the present mess,” Kane wrote in the Irish Times this week. Whether the party founded by a firebrand preacher is capable of compromise remains to be seen.