Sinn Féin’s breakthrough in Ireland’s general election was decades in the making, but not even Sinn Féin saw it coming.

Once a revolutionary party associated with guns and balaclavas, a toxic brand, it slowly edged from the fringe into the mainstream, inch by inch, and then on Saturday made a giant leap.

An exit poll gave Sinn Féin 22.3% of the vote, a statistical dead heat with Fine Gael on 22.4% and Fianna Fáil on 22.2%, two centrist rivals that have dominated Ireland for a century.

Full results are expected on Monday or Tuesday, but early tallies from count centres across Ireland on Sunday suggested the republican party had indeed made unprecedented gains and realigned Irish politics.

It did so in large part by appealing to voters who felt left behind by a booming economy and chafed at soaring rents, homelessness, insurance costs and hospital waiting lists.

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Its name can be translated as family or tribe of the Irish. A centre-right party with a socially progressive tilt. In office since 2011, first led by Enda Kenny, then Leo Varadkar, with support from smaller coalition partners. Traces roots to Michael Collins and the winning side in Ireland’s 1922-23 civil war. The party traditionally advocates market economics and fiscal discipline. Appeals to the urban middle class and well-off farmers. Fianna Fáil Its name means Soldiers of Destiny. A centrist, ideologically malleable party that dominated Irish politics until it steered the Celtic Tiger economy over a cliff, prompting decade-long banishment to opposition benches. Under Micheál Martin, a nimble political veteran, it has clawed back support and may overtake Fine Gael as the biggest party and lead the next coalition government. Founded by Éamon de Valera, who backed the civil war’s losing side but turned Fianna Fáil into an election-winning machine. Sinn Féin Its name means We Ourselves, signifying Irish sovereignty. A leftwing republican party that competes in Northern Ireland as well as the Republic. Traces roots to 1905. Emerged in current form during the Troubles, when it was linked to the IRA. Peace in Northern Ireland helped Sinn Féin rebrand as a working-class advocate opposed to austerity. Under Mary Lou McDonald, a Dubliner without paramilitary baggage, Sinn Féin has become the third-biggest party, and its vote share surged in the 2020 election. Others Partnership with Fine Gael during post-Celtic Tiger austerity tainted the centre-left Labour party. The political arm of the trade union movement, it is led by Brendan Howlin, a former teacher and government minister. The Social Democrats and Solidarity-People Before Profit are part of an alphabet soup of smaller, more leftwing parties. The Greens, wiped out in 2011 after a ruinous coalition with Fianna Fáil, have campaigned on the back of climate crisis anxiety and youth-led protests. Independent TDs have prospered in recent elections, turning some into outsized players in ruling coalitions. Rory Carroll

Many were young and wanted to shake things up, to deliver a black eye not just to Leo Varadkar’s ruling Fine Gael party but to the main opposition party, Fianna Fáil, which they deemed too crusty and complicit in the system they sought to change.

The great paradox is that unification with Northern Ireland, the cause that birthed Sinn Féin in its modern form and still defines it, barely featured in the campaign. Britain, Brexit, Boris Johnson were not even blips on the radar. For many in Dublin, Cork, Limerick and other towns, the troubles are about paying rent, not murky historical events north of the border.

It would be easy to depict this as the inevitable destination of a long march led by a savvy, mercurial guide, Gerry Adams. In 1986 he recognised that the IRA would not be able to bomb its way to a united Ireland and persuaded the republican movement to abandon its policy of abstention and to compete for – and take – seats in the Irish parliament, Dáil Éireann.

It was a lonely trek. In the 1987 general election, the party won 1.9% of the first-preference vote. In 1989, 1.2%. In 1992, 1.6%. Irish voters had no desire to elect people they associated with Semtex and corpses in the street.

Sentiment softened after the 1994 IRA ceasefire and the buildup to the 1998 Good Friday agreement. In 1997, Sinn Féin won 2.6% of the vote and got its first MP, Caoimhghín Ó Caoláin, elected to the Dáil. In 2002, that jumped to 6.5%, garnering five seats.

In 2007 it won 6.9%, in 2011 it took 9.9% and in 2016 it scored 13.8%, yielding 23 seats, making it about half the size of Fianna Fáil and Fine Gael. It was a steady rise that left the traditional FG/FF duopoly intact.

Few inside or outside Sinn Féin foresaw its breakthrough this week. Last year, after all, the party suffered big losses in European and council elections. Mary Lou McDonald, a Dubliner, had replaced Adams but struggled to enthuse the republican base and attract new voters.

With support slumping, the party fielded just 42 candidates for the 160-seat Dáil, a strategy to minimise losses. Then the campaign started and its popularity rose – and rose.

Varadkar tried to make the election about the humming economy and his record on Brexit but voters were fatigued with Fine Gael, in office since 2011, and jaded with Fianna Fáil, which had backed Varadkar in a confidence-and-supply deal.

The shock of the crash, when Ireland meekly accepted its austerity medicine, had ebbed, exposing anger at the cost of living and patchy public services. Young people who got a taste for voting in the marriage equality and abortion referendums were ready for something new.

Instead of a tide for the Greens – who appear to have done well, but not spectacularly – it turned into a wave for McDonald and colleagues such as Pearse Doherty and Eoin Ó Broin who articulated leftwing solutions to Ireland’s problems.

Fielding so few candidates, however, may cap the number of seats to around 30 – well below Fianna Fáil and Fine Gael – making Sinn Féin a contender to join but not lead a coalition. Both parties have ruled out entering into government with Sinn Féin but Dáil arithmetic may force U-turns or an FF/FG alliance, or a fresh election.

The republican slogan “tiocfaidh ár lá” means “our day will come”. Sinn Féin didn’t know that meant now.