After two years of deadlock and plenty of bad blood between London and Brussels and the Conservative government and the DUP, Rishi Sunak has sought to grasp the nettle and break the stalemate.
That impasse has bedevilled UK-EU relations and hobbled the power-sharing arrangement in Northern Ireland.
It is the boldest move of his premiership and laden with jeopardy.
Pull it off and this is a beleaguered prime minister very much emboldened.
Fail, and Mr Sunak could see his premiership sinking under the weight of Brexiteer rebellions, a resurgent Boris Johnson and continued tensions in Northern Ireland.
Where it was clear that Mr Sunak had won on Monday was with Brussels.
The bonhomie between the prime minister and the European Commission President Ursula von der Leyen was plain to see.
The PM hailed this as a "new chapter" in EU-UK relations while Ms von der Leyen - perhaps with her old adversary Boris Johnson in mind - claimed they had come out of these negotiations with a "stronger EU and UK relationship" and praised Mr Sunak's "very constructive attitude from the very beginning to solve problems".
A new principal, with a new approach, resulted in genuine gains with the EU moving in a way that many thought was not possible.
Mr Sunak won concessions that many Brexit watchers thought was not possible months ago when Mr Johnson conceived the Northern Ireland Protocol Bill in order to unilaterally overwrite the post-Brexit trading arrangements between Northern Ireland and Great Britain (a bill now dropped).
The new deal has a "green lane" with no checks for goods crossing the Irish Sea destined to stay in Northern Ireland, while a "red lane" would be used for goods continuing into Ireland and the EU single market.
The prime minister also said the agreement would end the situation where food made to UK rules could not be sent to and sold in Northern Ireland.
Under the new deal, Northern Ireland would have the same goods, drinks and medicines as the rest of the UK: "We have removed any sense of a border in the Irish Sea."
It also re-writes part of the existing protocol to allow Westminster to set VAT rates in Northern Ireland.
The deal also sought to tackle the "democratic deficit" which has so vexed unionists who will not countenance being treated differently to the rest of the United Kingdom and which has resulted in the suspension of the power-sharing assembly in Northern Ireland.
On Monday, the PM unveiled the "Stormont brake" which sought to address the issue of Northern Ireland being subject to EU goods laws.
Under a new arrangement, the Stormont assembly will be allowed to oppose new rules if a total of 30 members from at least two parties decide to activate the brake.
Mr Sunak said it was a "powerful new safeguard based on cross-community consent".
The question is whether the cross-community vote, requiring a majority of unionists and Irish nationalists, rather than a straightforward majority vote, will be enough to satisfy the DUP.
And while the PM told MPs that the deal removed 1,700 pages of EU law and "puts beyond all doubt that we have now taken back control", officials conceded too that the Windsor Framework doesn't remove EU law or European court jurisdiction from Northern Ireland.
And the key question to all of it is will the PM's gamble to grasp the nettle pay off? He has clearly won over Brussels and Ms von der Leyen, but he now has far more prickly characters to bring on board - and the outcome is still far from certain.
The DUP are predictably playing their cards close to their chest as we expected them to do.
DUP leader Sir Jeffrey Donaldson said that while "significant progress" had been made, "there could be no disguising the fact that in some sectors of our economy EU law remains applicable" and said the DUP would now pore over the details of the deal.
The unionists are also waiting on the legal advice and verdict of the European Research Group's 'star chamber' of lawyers who will pore over this deal as they did with that of Theresa May and Boris Johnson to see whether this deal restores British sovereignty.
Much rests on what the unionists decide.
As one senior Brexiteer put it to me this week, it would be "churlish" for a Tory MP not to back a deal if the DUP are satisfied.
Mr Sunak certainly won over some of his Brexiteers today.
One senior figure told me: "It looks pretty good and is better than I expected", while Northern Ireland Secretary and Brexiteer Chris Heaton-Harris and Northern Ireland minister Steve Baker urged colleagues to support the deal.
"I would resign if I felt I couldn't support the deal. So, you know, I'm backing this with a good heart," Mr Baker told Sky News on Monday night.
But there are rumblings too that this might not be the slam dunk Mr Sunak is hoping for.
When I asked one leading Brexiteer how significant it was that fellow travellers Mr Heaton-Harris and Mr Baker were satisfied, they replied that the pair "are just salesmen" and it was the job of the ERG to scrutinise this text.
"A quick read through makes clear the EU and ECJ applies to this deal," said this senior Conservative, adding that the threshold for the Stormont brake was too high.
"This is like a budget. It sounds good on day one until the detail begins to unravel it," they said.
As for Mr Johnson, he is also biding his time to see how this deal is absorbed. Sources close to him say the former prime minister "continues to study and reflect on the government's proposals".
No 10 are delighted at how the day has gone, with one senior figure telling me "it couldn't have gone better".
This is a watershed moment that could prove not just a breakthrough for restoring power sharing in Northern Ireland but in resetting relations with the EU and Mr Sunak's premiership too.
So far, he has been an underwhelming prime minister who has failed to impress his party or the public. Pull this off and he might get that honeymoon that eluded him when he was handed the crown last autumn.
What's clear is that Mr Sunak needs something momentous to move him from being a caretaker prime minister squatting in No 10, to a credible one who has at least a shot of turning around the Tories' fortunes before the 2024 election.
He and his team know that finally threading the Brexit needle where those before him failed would be a very good start.
The question is, will his enemies let him?