Michelle O'Neill should be careful what she wishes for... if there is no majority for Irish unity in the next five years, chances are there never will be
Sinn Fein's hopes for a referendum by 2023 depend on Brexit going badly and swathes of 'nationalists' previously indifferent to reunification changing their minds
It is hardly surprising that Michelle O'Neill is calling for a border poll. If she had not urged a vote on a united Ireland, that would have been read by some as a softening of the Sinn Fein position after the departure from high office of Gerry Adams. Suggesting that it come within five years makes sense from her perspective.
The deciding factor for many will be the outworking of Brexit. That should be clear enough by 2023. An earlier vote would not capitalise on Brexit, because then no one would be sure yet whether it had worked out well or not.
If she is thinking there are many people in Northern Ireland who would hold on to the Union with Britain for another couple of years to see how things work out, then she is probably right.
If by then the economy has slumped badly and the border has returned as a significant irritant, she may have a better chance of getting the result she wants.
On the other hand, the Tories may have fragmented by then, we might have the softest possible Brexit and Labour might be back renationalising the railways, bolstering the health service and scrapping Trident, and what would it be but bliss to be alive in such a dawn?
Who knows? Things are too uncertain now for a vote that would work to Sinn Fein's plan.
But give us a Britain outside the EU, having lost its bearings in the world, looking like it might be perpetually Tory - especially if Scotland leaves the Union - and following from that you get a further erosion in support for social services and the NHS and many will wonder what would be lost by pitching in with the south.
For how long would we really be able to boast of having a better health service here?
Complicate all that with a sense that reconciliation at party-political level is simply a lost hope and the confidence of Arlene Foster that a united Ireland could never happen would look misplaced.
She told Patrick Kielty she wouldn't want to live in it.
It would hardly be more uncomfortable than living in the socially conservative, Bible-bound, stunted little Ulster she offers the rest of us.
But if she wants an Ulster that is comfortable inside the UK, even a post-Brexit UK, then she should be talking to Theresa May about the state of health and education here and gambling that most people will, when faced with a choice, vote pragmatically.
She, of course, will not vote pragmatically, but with her heart devoted to Britain and her monarch.
If nationalists prove as sentimentally attached to their affronted Irish identity after Brexit, her struggle will be even harder.
She may hope that most people are lot like herself. We don't know.
The Belfast Telegraph online poll suggests that 18% of us would have to change our minds to deliver Irish unity at a referendum.
Given that even at the most crucial constitutional vote in modern times, after the Good Friday Agreement, 20% of voters didn't even show up, that leaves something to play for.
About 15% of Scots didn't even bother to vote in an independence referendum in 2014.
But Irish unity in the next decade depends mostly on a window that may not open and may close very quickly.
Brexit is crucial to this.
The IRA campaign for decades failed to sway significant numbers in favour of a united Ireland, because republicans could not provide a practical argument for it.
People could see there was a problem, but for many, perhaps most, the greater part of that problem was the IRA itself. In fact, the IRA masked the degree of nationalist interest here, because many who want a united Ireland were embarrassed to say it for fear of being associated with people who thought they could advance that cause by murder and sabotage.
After the Good Friday Agreement, nationalism grew and raised the Sinn Fein vote.
The greatest drag on Sinn Fein had been the very IRA it so fervently celebrates.
Which takes us back to letting republicans bear the burden of their own anomalies. They are welcome to it.
For the rest of us, this growth in confident nationalism did not pose the significant threat to the Union, because sufficient numbers of people in the supposedly nationalist community weren't nationalists at all; they were de facto unionist.
They were crucial to stability here, but they were invisible on the political landscape, because unionism which relied on them for survival made no space for them.
They were never going to be unionists like Arlene. They might take a day off work to watch a royal wedding, but for them that was like staying in at night to see a much-hyped episode of EastEnders. Royals are just celebrities to them.
Unionism lost the moment at which it could extend its social and cultural boundaries.
Though it relied on the de facto unionists to hold the Union together, it did nothing to identify with them and gave them no credit for being the cornerstone of the Union.
There was a way to sell Britishness as multicultural, multilingual, connected to the world, liberal and modern. The idea was aired briefly in the 1990s, but nobody really tried.
The DUP decided that it was more important to preserve party unity around evangelical Christian principles than to grow into a party that could govern for all.
In confining itself within a laager, it made itself an easy target for Sinn Fein, which could pick up any of half-a-dozen common sense issues and taunt them with it.
But Sinn Fein has difficulties, too. It invests all its hopes now on the border poll and those hopes depend on Brexit going badly and so insulting those in the north who identify as Irish will want to withdraw from the UK.
The vote depends, crucially, on the section of the "nationalist" community that hasn't really wanted a united Ireland changing its mind.
These are people who will not have been traditional Sinn Fein voters. They have probably been voting for the SDLP, Alliance, or nobody at all.
If they can be roused by the shock of a hard Brexit combined with the continued intransigence of the DUP, a republican miracle might be possible.
Michelle O'Neill would be well picking her moment with care because if in such favourable circumstances, there is no significant surge in demand for Irish unity, she may have to resign herself to the prospect that there never will be.