Sinn Féin held on to all seven of its seats at Westminster in the 2024 election, making it the largest Northern Irish party in the UK parliament, the Northern Ireland Assembly, and in local government in Northern Ireland.

Although Sinn Féin refuses to take seats in Westminster, declining to swear an oath of allegiance to the crown, its result provides a significant boost for Irish nationalism. It also raises hopes of a border poll on whether Northern Ireland should reunify with the rest of the island of Ireland sometime in the 2030s, even though the unionist bloc vote (across multiple parties) is still slightly larger than the combined nationalist vote in Westminster.

Going into the elections there was an expectation that Sinn Féin would emerge as the largest party due to the fragmentation of the unionist vote. But it also managed to increase its majorities in all seven constituencies.

That the party was able to do this despite a historically low turnout of 57% suggests that its activist base in the North has an impressive ground game that can motivate potential voters to come out on election day. Even formerly marginal seats for the party now provide comfortable majorities for Irish nationalism.

In Fermanagh and South Tyrone, the party’s decision to run Pat Cullen, the former head of the UK’s nursing trade union, has paid dividends. Sinn Féin’s majority increased significantly – from 57 votes to 4,571 – despite facing the UUP’s Diana Armstrong as a single unionist candidate.

This mutually beneficial relationship between Sinn Féin and organised labour on the island of Ireland is likely to continue over the coming years as the trade union movement seeks alternatives to the struggling Irish Labour Party.

In East Derry, Kathleen McGurk came within 179 votes of taking the seat held by the DUP’s Gregory Campbell, which would have been a severe blow to that party and to wider unionism. In Foyle, Sinn Féin reduced the majority held by the leader of the SDLP, Colum Eastwood, making this a prime target seat for the next general election.

Meanwhile, in the Republic of Ireland

In contrast to these latest results, Sinn Féin had a disappointing set of local and European elections in the Republic of Ireland in June. The party did increase its overall number of local councillors but it had hoped to emerge as the largest force in local government. Instead, with 11.8% of the vote it came in a distant third place to its main rivals of Fianna Fáil and Fine Gael. In the European elections, it won only two seats with 11.1% of first preference votes, and none of its candidates topped the poll in any constituency.

So, what explains Sinn Féin’s differing fortunes between Northern Ireland and the Republic of Ireland? Following on from its breakthrough 2020 general election in the Republic of Ireland, Sinn Féin built a coalition of anti-establishment voters consisting of the working class and disaffected middle-class youth. The party’s appeal was based on a relentless focus on the housing crisis and a promise of change to the status quo.

By July 2022, Sinn Féin reached a high of 36% in opinion polling. However, it has now dropped to the low twenties in most recent polls.

The rise of anti-immigrant sentiment – fuelled by the continued housing crisis and increased asylum applications – has fractured the uneasy coalition of voters that formed in 2020. Like other mainstream Irish parties, Sinn Féin supports a relatively liberal immigration policy.

This damages its support among those voters who hold anti-immigrant views. But the far-right claims that Sinn Féin supports “open borders” and by counteracting this accusation it may also be losing voters that are concerned about the growth of anti-immigrant rhetoric.

Additionally, flip-flopping on issues like the expulsion of the Israeli ambassador and state-led reductions in Dublin house prices has alienated voters on the left.

Immigration has accelerated Sinn Féin’s decline in the polls, but there are wider, longer-standing issues with electoral strategy. In response, the party is divided over whether to tack towards the centre or continue with a more left-wing populist message.

Turnout was low in the local and European elections at around 50% and lower again in many urban working-class constituencies where Sinn Féin votes are concentrated. There is an issue with Sinn Féin’s ability to get its base out in the Republic of Ireland, especially for these second-order elections that are less important to many voters.

Exit polling also shows that only 18% of voters had met a Sinn Féin party candidate, much less than either Fianna Fáil or Fine Gael. This lack of contact matters in Ireland’s personalised political culture and it suggests that Sinn Féin may not be effectively using its activist base in the Republic of Ireland.

Incumbency also matters in local elections where a candidate’s name recognition among voters is likely to be low. Sinn Féin’s continued lack of a significant local councillor base hurts its organisational ability and its local TDs (members of the Irish parliament) are just not stepping into this leadership vacuum on the ground.

Sinn Féin previously recovered from a disappointing local election in 2019 to gain the largest vote share in the 2020 general election. It could do the same in the next general election expected sometime this autumn.

Sinn Féin representatives now argue that their 36% position in the polls was unsustainable. But there will be anger in the party if it fails to win a vote in the next general election at least equal to its 2020 share. Sinn Féin’s leadership has already moved senior party officials to the Republic of Ireland to help recreate the party’s success in Northern Ireland – and to address the gaps in the party’s organisational ability between north and south.