LONDON — Boris Johnson may have coined the phrase, but Rishi Sunak hopes he’s the man who can finally claim to have “got Brexit done.”

The British prime minister will on Monday host European Commission President Ursula von der Leyen in what’s being sold by No. 10 Downing Street as the pair’s “final talks” on resolving the long-running row over post-Brexit trading arrangements in Northern Ireland.

Downing Street has drawn up a carefully choreographed sequence of events following the meeting. Sunak will brief his Cabinet following the late lunchtime face-to-face with the European Commission chief.

He then hopes to hold a joint press conference with von der Leyen to announce any deal before heading to the House of Commons late on Monday to begin his trickiest task yet — selling that deal to Brexiteer MPs on his own Conservative benches, many of whom will be closely watching the verdict of Northern Ireland’s Democratic Unionist Party (DUP).

It’s likely to mark a defining moment in Sunak’s young premiership, which only began in October when he took over a Conservative Party still riven with divisions following the departures of Johnson and Liz Truss in quick succession. If successful, he will hope to draw a line under the rancorous follow-up to Britain’s 2020 departure from the bloc, and herald an era of closer cooperation with Brussels.

But even as Downing Street was drawing up plans for Monday’s grand unveiling, members of Sunak’s own party were voicing skepticism that the prime minister will have done enough to win their backing. And without DUP support, Northern Ireland’s moribund power-sharing assembly could remain collapsed.

Testing times

Since taking office, Sunak has put securing a deal with Brussels on the so-called Northern Ireland protocol near the top of his to-do list.

The post-Brexit arrangement has been a long-running source of tension between the U.K. and the EU, and the two sides have been locked in months of talks to try to ease the operation of the protocol while addressing the concerns of both the DUP and traders hit by extra bureaucracy.

Under the protocol, the EU requires checks on trade from Great Britain to Northern Ireland in order to preserve the integrity of its single market while avoiding such checks taking place at the sensitive land border between Northern Ireland and the Republic of Ireland.

But the DUP sees the protocol as separating Northern Ireland from the rest of the U.K. and is boycotting the region’s power-sharing government until changes are made.

In a statement Sunday night, Downing Street said Sunak wanted “to ensure any deal fixes the practical problems on the ground, ensures trade flows freely within the whole of the U.K., safeguards Northern Ireland’s place in our Union and returns sovereignty to the people of Northern Ireland.”

Downing Street has kept the detail of any deal a closely-guarded secret. In an interview on Sky News Sunday, Deputy Prime Minister Dominic Raab talked up the prospect of “more of an intelligence-based approach” to goods checks, and a move away from individual checks at Northern Irish ports. The U.K. and EU have already talked up more access for Brussels to British goods data.

One of the biggest flashpoints for Brexiteer MPs and the DUP will be the status of the Court of Justice of the European Union in governing disputes under the protocol. They see the continued presence of the EU’s top court in the arrangement as a challenge to British sovereignty.

On Sunday, Mark Francois, chairman of the European Research Group of Conservative Euroskeptics, set a high bar for his support, warning any deal must see Northern Ireland treated on the “same basis” as the rest of Great Britain. He warned that even a reduced role for the CJEU over Northern Ireland was not “good enough.”

Raab told Sky that scaling back some of the regulatory checks and paperwork “would in itself involve a significant, substantial scaling back of the role of the ECJ,” and he talked up the idea of a “proper democratic check coming out of the institutions in Stormont,” the home of Northern Ireland’s power-sharing assembly.

Minefield

One potential source of Brexit trouble on Sunak’s benches is Johnson himself, who has already been warning the prime minister not to drop the Northern Ireland Protocol Bill aimed at allowing U.K. ministers to unilaterally sideline the arrangement.

The Sunday Times reported that Johnson, while being lobbied to support a deal to cement relations with U.S. President Joe Biden, responded with the colorful retort: “F*** the Americans!” The same paper cited a “source close to” Johnson who dismissed it as “a jocular conversation in the [House of Commons] chamber that someone evidently misunderstood.”

As another defining Brexit week begins, Sunak appears willing to plow ahead, even without the support of the most hardline Brexiteers in his party. Raab insisted on Sunday MPs would “have the opportunity to express themselves on the deal,” but did not elaborate on whether there will be a House of Commons vote on the arrangement.

Former Chancellor George Osborne, one of the key figures in the campaign to remain in the European Union, urged Sunak to press on and “call the bluff” of the DUP, Johnson and the ERG — or his premiership would be “severely weakened.”

“Having got to this point in the minefield, he has to proceed,” Osborne told the Andrew Neil Show.