Since entering into a 'confidence and supply' deal to prop up the Tory government in June, the DUP has undergone a transformation. What was once a peripheral party of limited influence holds the balance of power at Westminster. And now they have demonstrated their ability to challenge Theresa May over Brexit.
As last week's desperate thrash to secure a deal on the Irish border showed, the DUP had only to raise its objections to the proposed draft for the whole thing to be temporarily derailed.
It was only after DUP concerns about Northern Ireland retaining "regulatory alignment" with the EU were at least partially assuaged that the negotiations got back on track and the breakthrough between the UK and the European Union was reached.
The deal was even sweetened by some traditional Ulster-style fudge: a distinct lack of specifics about the way the border will actually be managed. How a soft border can be delivered without the UK remaining in the single market and customs union remains unknown.
There are still numerous other unanswered questions, of course, not least why Theresa May ever thought - if indeed she really did - that the DUP would be willing to tolerate a deal which appeared to treat Northern Ireland differently from the rest of the UK. After all, Sammy Wilson had made the point, using almost exactly these words, just a few days before.
The mystery deepened when Arlene Foster claimed that she had been asking for information on the British Government's plans for the Irish border for five weeks, but had only received news of the proposed arrangement last Monday morning.
So how do leading UK commentators view the DUP's role in the Brexit talks, from the chaos of Monday, to the uneasy resolution achieved by Friday? What do they make of this small, strident band of unionists from Northern Ireland who find themselves at the very centre of Brexit negotiations?
"Hats off to the DUP, they played a blinder," exclaims Daily Mail columnist Quentin Letts. "They said, 'up with this we will not put'. There was no particular grandstanding, and I liked the fact there was no public whinging against the Tories. It's perfectly possible to criticise the DUP for their views, but you can't accuse them of lacking seriousness."
Matthew Parris, the Spectator columnist, gives me a very different view. He found it incredible that the DUP was unaware of the initial proposed deal with the EU. "I suspect the DUP knew more than they say - they just couldn't miss an opportunity for grandstanding," he says.
Helen Lewis, deputy editor of the New Statesman, agrees: "I did wonder if it was a choreographed move, to sell it to their constituents, getting concessions out of the UK."
And Patrick Kidd, the Times' parliamentary sketch writer, also says it seemed strange that May and her advisers hadn't anticipated that the draft deal would be a problem.
"The cynical part of me wonders if it was scripted," he says. As for the agreed deal itself, John Rentoul, the chief political commentator for the Independent, considers that the DUP were uncharacteristically accommodating "given the DUP's capacity for saying no, and continuing to say no when they might compromise - they are normally prepared to bring the whole thing down." He too sees it as "a bit of theatre" intended for their domestic audience.
But Rentoul has no doubt that the DUP is in a very good position.
"They have been given a veto over the trade negotiations, complete control over whatever is agreed. They just have to sit tight and negotiate hard". Meanwhile, John Crace, the Guardian's sketch writer, has no truck with the suggestion that Theresa May was doing a spot of grandstanding of her own.
"For me, the idea that [May] would go through the rigmarole of facing off the DUP just to look tough is a conspiracy too far. She actually looked desperately wounded by the whole thing."
Crace says that the events of the last week "do quite clearly show that the Brexit negotiations are as much about Tory party management as they are about national interest, which is a huge cause for concern. A tough prime minister would have faced off the DUP and their 10 MPs. But the DUP thought she was too weak to do it, and she is".
Letts says that opinions on the DUP, both at Westminster and beyond, have shifted in recent years.
"Twenty years ago a lot of people thought they were a little bit hairy. They're now seen as mainstream as far as unionist opinion goes. On the Conservative side, they are seen as allies but not necessarily as friends. Of course, pro-Brexit Tories were incredibly grateful to them this week."
Letts says that in the Commons tea room in recent days, there was a lot of comradeship towards the DUP from backbench Tories. "They say, 'the DUP says what we can't'".
Having seen them in action at Westminster this week, Kidd says that the DUP seemed in a smug mood.
"Yes, very confident and cocky. Ian Paisley was literally flexing his biceps," he says.
Summarising the public perception of the DUP, Parris says: "Formidable, but entirely focused on their own advantage."
And Lewis tells me: "When the supply and confidence deal was signed, a lot of people said - who?
"They were an unknown quantity. Some of the Westminster commentariat see them as bumbling and provincial, but they are ruthless and skilful. They are also a small caucus which is relatively disciplined, and while they are not ready to use the nuclear option - bringing down the government and ushering in a Corbyn government - they will do everything up to that."
Crace says the DUP was previously seen as "a peripheral, noisy, reactionary group" but since the general election they have been acknowledged as "tough negotiators".
Indeed, last month Nigel Dodds was named top negotiator at the Spectator's Parliamentarian of the Year awards.
"They're not just a sideshow if they can derail a deal by four days," points out Crace.
Rentoul says that the mainstream liberal media see the DUP as "the work of the devil, a dinosaur throwback to the 16th century".
"It does annoy me," he says. "Since Ian Paisley [senior] at his worst, they have come a long way. They have done quite well in presenting themselves as reasonable."
Commentators may vary in their assessment of the DUP, its motivations and its ability to deliver the Brexit deal it wants. But they are agreed on one thing, summed up by Kidd.
"The DUP are part of the story now, when they never were before," he says.