After Eamon Gilmore’s resignation, Karl Marx’s quip remains indispensible: everything in history happens twice, the first time as tragedy and the second time as farce. The first time Labour surrendered its political space to Sinn Féin was when it stood aside in the crucial 1918 general election. Its mistake was tragic in that it missed a moment in which Irish politics was radically reshaped and took a form that it would hold for almost a century – until the general election of February 2011 to be precise.

The second time Labour opened the door to Sinn Féin was in the aftermath of that election when Gilmore finally had the opportunity to realign Irish politics by building a serious and radically democratic opposition to the imposition of banking debts and so-called austerity on ordinary citizens. This time, its response was farcical rather than tragic. Farces are driven by the lusts of middle-aged men. In this case, the lust of Labour’s ageing leadership was for power, not sex – it traded the party’s historic long-term opportunity for the immediate and shallow pleasures of one last spin on the merry-go-round of office.

Assumption The one compliment the Labour leaders deserve is the assumption that they knew exactly what they were doing. Immediately after the 2011 election, I wrote here that if the party went into government without a radical renegotiation of the bank deal and the troika programme, "Labour will be devoured from two sides, its radical support eaten by Sinn Féin, the United Left Alliance and independents and its 'respectable' support consumed by Fine Gael. The voters who were ruthless enough to decimate Fianna Fáil will think nothing of decapitating Labour." (The ULA has since dissolved into its constituent parts and has indeed devoured much of Labour's base, especially in Dublin.)

This was not dazzling insight. It was a mere statement of the obvious – obvious, that is to say, to Eamon Gilmore and his senior colleagues. They knew very well that they were destroying the Labour Party and with it the honourable social democratic tradition it represented. They decided to do it anyway.

There are of course large differences between 1918 and 2011. Ironically, in the first case, Labour screwed up by standing aside; in the second case by not standing aside. But each was a defining moment in which wrong decisions had long-term consequences that could be summed up in two words: Sinn Féin.

It has taken just three years for Sinn Féin to turn the logic of what Labour did in 2011 into stark electoral numbers. They are quite staggering: in 2011, Labour’s vote was twice Sinn Féin’s. In 2014, Sinn Féin’s was nearly three times Labour’s. In terms of the ownership of the mainstream left-of-centre space in Irish politics, this shift seems definitive. The only qualification is that Sinn Féin is still perfectly capable of screwing up its own prospects.

At a number of levels, Sinn Féin’s operation south of the Border has been hugely impressive. It deserves great credit for what it has not done: exploiting anti-immigrant and anti-Traveller prejudice in a way that would have yielded quick dividends. (Sinn Féin is the reason that Ireland, almost uniquely, does not have a far-right populist party.)

It has taken gender balance far more seriously than any of the other main parties. It has done a superb job of bringing new, younger candidates and activists into politics. It has articulated, especially through Pearse Doherty, a substantial critique of the bank bailout. After a very poor start, it has enormously improved its performance in the Dáil. These are real democratic achievements.

But the pre-democratic past hasn’t gone away, you know. The old leadership still seems obsessed with seeking a retrospective endorsement from the southern electorate for its morally catastrophic campaign of violence. The irredentist side of the party is still focused on using power on both sides of the Border to force through a referendum on a united Ireland that would achieve nothing except a possible reignition of sectarian conflict.

Broken ranks There is something creepily cult-like in the fact that not a single party figure has broken ranks on Gerry Adams's claims not to have been in the IRA, even though last week's Irish Times poll showed that nearly 60 per cent of their own voters don't believe he's telling the truth. And it remains far from certain that the party has a fixed left-of-centre identity: it hovers between being the new Labour Party and being just a greener version of Fianna Fáil. (In RTÉ's exit poll, 29 per cent of Sinn Féin's voters said they would like it to coalesce with left-wing parties but 35 per cent opted for Fianna Fáil.)

These unresolved questions mean that Sinn Féin’s position as the successor to Labour in southern politics can’t yet be taken for granted. A broad progressive movement will thrive if it can bring together four big issues – debt resolution, radical democratic reform, social justice and sustainable economic progress – in a coherent vision.

Sinn Féin’s great strength is that Labour has ceased to be a credible vehicle for that vision. Its great weakness is that its own vision is still distracted and obscured by feverish imaginings and haunting shades.