BELFAST — In Northern Ireland, pro-Brexit unionists insist the general election isn't really about Europe. Their opponents disagree.

The Democratic Unionist Party's strong performance in the 2017 election, when it won 10 seats in the House of Commons, gave it a strong hand and allowed it to prop up a minority conservative government. But they go into this election having been unceremoniously dropped by Boris Johnson, who signed off on a Brexit withdrawal deal with the EU that would effectively create a barrier in the Irish Sea, a clear breach of the DUP's "blood red line."

Pro-Remain nationalists want to make the election in Northern Ireland all about London's Brexit betrayal, and Sinn Féin leader Mary Lou McDonald pitched her party's manifesto as a rejection of Brexit and of Westminster (Sinn Féin doesn't take its seats in the Commons.)

"In this election is important that people use, that people lend, that people borrow votes from others, to ensure that loud and clear again it is heard the north has not consented to Brexit, the north has not and will not consent to Brexit," McDonald said.

But DUP leader Arlene Foster told POLITICO domestic issues were "very much at the top of the agenda” on the doorstep after thousands of healthcare appointments were canceled in the middle of the election campaign when nurses went on strike.

A recent poll carried out by LucidTalk shows support for the DUP has stayed strong, with projections suggesting it will remain the biggest party on 28 percent

It is a striking contrast to the campaign run by Johnson, who has labeled his manifesto Get Brexit Done and brings every topic he can back to the U.K.'s EU departure. In contrast Northern Ireland's only pro-Brexit party has made health, education, jobs, childcare and protecting the vulnerable the focus of its own manifesto. In short, anything but Brexit.

In a country where voting preference for the majority of people is first and foremost dictated by whether you support being part of the United Kingdom or part of a united Ireland, getting out the core base is crucial to the electoral success of the DUP and Sinn Féin, the country's two main parties.

Last time around both were successful. Voters shunned the more moderate nationalist Social Democratic and Labour Party and Ulster Unionist Party, giving the DUP and Sinn Féin all but one of Northern Ireland's seats in the Commons (the Conservatives, Labour and the Liberal Democrats don't field candidates in Northern Ireland.)

A recent poll carried out by LucidTalk shows support for the DUP has stayed strong, with projections suggesting it will remain the biggest party on 28 percent. But it faces local threats in a clutch of Belfast seats after the pro-Remain SDLP, Sinn Féin and Greens formed an anti-Brexit tactical voting pact.

Nigel Dodds, the DUP's deputy leader, faces a fight to fend off Sinn Féin’s John Finucane in Belfast North in what appears to be a knife-edge contest, while the SDLP’s Claire Hanna is polling ahead of the DUP's Emma Little Pengelly in Belfast South.

"We are getting our vote out, that is the only way we can do it," one DUP candidate, who didn't want to be named, said when asked about the prospects of Dodds keeping his seat.

Blame Boris

The DUP has had quite a fall from grace since Johnson became Tory leader.

When Theresa May failed to secure a Commons majority in 2017, she turned to the DUP and they signed a confidence-and-supply agreement that included extensive financial support for Northern Ireland.

Its 10 MPs appeared to wield huge power over the Tory government's Brexit strategy under May, who was sent back to the negotiating table in Brussels last December when the DUP took umbrage at an original plan to achieve "sufficient progress" in the first phase of talks, which included a Northern Ireland-only backstop. Even her eventual deal with the EU, which included a plan for an all-U.K. customs backstop if the future relationship threatened to create a border in Ireland, was rejected in parliament thanks in part to DUP lobbying.

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With May gone and Johnson as prime minister, things took a turn for the worse for the DUP. Despite Johnson's assurances he would never create a border down the Irish Sea, he eventually agreed a deal with the EU which will require checks on goods traveling between Great Britain and Northern Ireland. Johnson has denied claims that there would be such new customs checks but a leaked government analysis suggests that "at a minimum exit summary declarations will be required when goods are exported from NI to GB."

The DUP candidate insisted that despite the party's failure to clip Johnson's wings, support for the party at home is holding up. "They recognize the DUP did use its votes to block the deal. Boris hasn't been able to get it through [parliament]. They realize that there is a strong possibility Boris will win the election, but they are not blaming us for that," the candidate said.

The DUP also thinks the lack of a working Northern Ireland Assembly will get its voters to the ballot box. Under the terms of the Good Friday Agreement, the largest unionist and nationalist parties must govern together but they haven't done so since early 2017 when Sinn Féin walked away over a botched renewable heating scheme. The nurses strike has increased calls for the restoration of power sharing as the assembly is responsible for healthcare in Northern Ireland.

It is not just in the short term that Northern Ireland's nationalists hope for electoral success. They are also eyeing a referendum on whether Northern Ireland should remain part of the U.K. or become part of a united Ireland.

Legislation passed in Westminster in July which required the government to change abortion laws and extend same-sex marriage to Northern Ireland if devolution was not restored by October is also occupying DUP voters' minds.

In one of the DUP's heartland seats, where POLITICO went door-knocking with a local candidate, one of the few voters at home on a Tuesday afternoon raised the issue as his number one election priority. The voter was a Brexiteer but told the candidate that Europe "pales into insignificance" compared to the social upheaval of changing abortion and same-sex marriage laws.

A fresh round of talks to get the Northern Ireland Assembly up and running again is due to be held on Monday.

The Brexit message

While the DUP sells its domestic message to its base, Northern Ireland's pro-Remain parties think Brexit is the key to electoral success.

Sinn Féin and the SDLP each agreed to stand aside in three seats to give pro-Remain rivals a chance to oust the DUP.

Finucane, who is standing against Dodds in North Belfast, claimed voters are facing "a threat in the form of Brexit, that is posing a very serious risk and immediate risk, not just the our economy and our way of life, but also a risk to the Good Friday Agreement."

"In my constituency they have an opportunity to remove an MP who has revelled in being a Brexiteer; has been part of the Vote Leave campaign; has stood over Brexit and all of its disaster since 2016. And I think people want to make him answer for those politics," Finucane said.

But it is not just in the short term that Northern Ireland's nationalists hope for electoral success. They are also eyeing a referendum on whether Northern Ireland should remain part of the U.K. or become part of a united Ireland — often termed a "border poll."

As part of the Good Friday Agreement, a border poll should be called by the U.K.'s Northern Ireland secretary if it appears a majority of voters want Northern Ireland to cease being part of the United Kingdom and form part of a united Ireland instead.

“There’s a conversation underway here on this island that people have never witnessed before, and that’s a hugely positive thing,” said Michelle O'Neil, vice president of Sinn Féin. “There are people out there who perhaps never before have considered [and] are now considering the constitutional position. They’re thinking about their own interests. That’s how people vote, and rightly so.”

Colum Eastwood, leader of the SDLP, agrees that a Johnson government “destabilizes the place, which makes people want a united Ireland more.” But he warned against "headlong rushing into a referendum," saying there was more policy work needed before a poll should be held.

But Foster dismissed the suggestion that London's handling of Brexit could help the nationalist cause.

"It is not a question of whether Boris wants us or not. We are British citizens, and therefore we are entitled to be treated the same as every other part of the United Kingdom. We're not second class citizens in any way, therefore it's not a question of whether they like us, or whether they don't like us. It's a question of respecting our British citizenship," she said.