Adams' departure as SF leader is now a little closer no matter election outcome
And then there were three. Regardless of how the investigation into the 1972 murder of Jean McConville proceeds, Gerry Adams can surely be added to the list of party leaders – already containing Eamon Gilmore and Micheal Martin – whose future may depend on the outcome of polling on May 23.
For all Sinn Fein's protestations that Adams voluntarily presented himself for interview and the claims that the timing of his arrest was politically motivated, this is a potentially disastrous development for the party and its leader.
Just when Sinn Fein seemed to be on a cusp of smashing through the ceiling that limited its support for decades comes the most vivid reminder of the party's bloody past.
The process of "normalisation" of Sinn Fein is critical to attracting middle-class voters. The party won't forsake its republican roots: the goal of a united Ireland remains, however elusive it might seem, but nowadays it's the bread and butter, everyday political issues that drive Sinn Fein. And the party is good at them too.
In the North, it has shown itself to be a more than capable administrator. Pragmatism is the order of the day, be it implementing cuts in spending or raising a toast to the British queen.
South of the border, Sinn Fein is rapidly benefiting from the damage done to Fine Gael, Fianna Fail, Labour and the Greens by six years of austerity budgets. A younger generation of TDs, best personified by the hugely impressive Mary Lou McDonald, is bringing support in areas where the party previously endured what was akin to pariah status.
But 'normal' political parties don't have leaders who are arrested in connection with the abduction, murder and disappearance of a mother of 10. Sinn Fein can hardly emerge unscathed from that.
It's 20 years in August since the IRA ceasefire. There's a generation of voters out there who never knew the Troubles. And even for those who were around, memories are fading.
But Adams' arrest brings the horrors of the conflict back into the public consciousness – just three weeks before local, European and by-elections.
For the first time in a long time, Sinn Fein is on the back foot; angry and defensive. McDonald in recent weeks and months has been the star political performer in the State, brilliantly skewering Rehab and CRC senior figures at the PAC and berating government ministers. She cut a very different figure on radio yesterday morning.
Her angry claims of political manoeuvring in relation to the timing of the arrest came across as conspiratorial and a little desperate. It also sounded too like the Sinn Fein of 30 years ago for comfort.
Of course McDonald has to back Adams. But it still sounds ludicrous to hear her insisting that she believes her leader when he says he was never in the IRA. There's an old adage in politics that when you're explaining, you're losing and Sinn Fein is having to do some serious explaining all of a sudden.
Senior figures dismiss out of hand suggestions that Adams' leadership is on the line. But it must be.
Sinn Fein is different from other political parties. There won't be a heave against Adams. For many in the party, Adams is Sinn Fein. The only possible comparison in Irish political history is with De Valera and Fianna Fail. And Dev led that party until he was 76.
Those who talk about how Sinn Fein would attract more support in the South with Mary Lou as leader aren't wrong. But this ignores the reality that, such is Adams' stature in republican circles, he is almost untouchable. Almost.
Even De Valera was eventually eased out to make way for Lemass, when it became obvious that the electorate saw him as out of touch.
Nobody can be sure yet how voters will react to Adams' arrest. But if, in the days after polling, Sinn Fein has underperformed in the locals or hasn't won a seat in say Dublin and/or in Midlands-North West, it will be put down to one reason and one reason only.
The narrative will be: before the arrest, Sinn Fein was on its way to three Euro seats and 20pc in the locals, but Adams had proved a significant liability.
That might be highly simplistic – none of the Euro seats, for example, were in the bag – but it's how it will be seen.
Sinn Fein would never be seen to respond to media calls for a change at the top. If anything, it would do the opposite. Unlike if Labour or Fianna Fail implodes on polling day, nothing will happen straightaway or even for months.
There won't be party figures calling for Adams to consider his position or a no-confidence motion – that military discipline still exists. But behind the scenes, talks will be taking place. Adams, more than anyone, will know if the time has come to make way.
A lot depends on May 23. Of course, if there are any further developments today, then all bets are off. But even if there aren't, the suspicion is that the day of Mary Lou McDonald's succession has been moved forward.
Shane Coleman is presenter of 'The Sunday Show' on Newstalk 106-108FM