Four years ago, Sunder Katwala wrote in The New Statesman about “The Farage Paradox” – that the more media exposure the Ukip leader got, so there was a corresponding dip in support for leaving the EU.
The most zealous exponent of taking the UK out of the European Union was soaring in the polls and his party was a greater threat to the political establishment than had ever been the case.
But at the same time, support for that party’s ultimate goal was not - as one might have expected - moving in tandem with support for Ukip.
Farage, unsurprisingly, did not agree with the hypothesis and when the EU Referendum was called he expected to be at the centre of the Leave campaign.
But Dominic Cummings, the maverick genius at the heart of Vote Leave, had formed a similar conclusion to Katwala, as had Douglas Carswell, the Tory MP who would defect to Ukip, after analysing detailing polling.
In Tim Shipman’s magisterial book on Brexit, All Out War, Carswell is quoted as saying: “You see Ukip taking off, disapproval of the EU going down. It’s a direct correlation.”
While recognising Farage’s strengths in appealing to parts of the country unreachable to any other politician, Cummings decided to keep Farage as far away from the official Leave campaign as possible.
A similar situation arose in the 2017 Assembly election where Arlene Foster actually increased the DUP’s vote, despite the RHI scandal - yet drove a far greater surge in support for nationalist parties, meaning that unionism lost its Stormont majority for the first time in the history of Northern Ireland.
And this week there has been further evidence that the same rule applies to Sinn Féin.
No party on the island of Ireland is more committed to the idea of Irish unity. Many members of Sinn Féin were prepared to kill – and spend large portions of their lives in jail as a result – in an attempt to force a united Ireland.
Yet that party is now arguably an impediment to republicans ever winning a border poll. Some republicans will point to Sinn Féin’s remarkable electoral success as evidence against that proposition.
But, as The Farage Paradox demonstrates, electoral success within a limited segment of the population – Sinn Féin’s highest ever vote was 29.4% in the 2017 General Election – is not necessarily an indicator of ability to win more than 50% of the vote in a referendum.
What appeals to a core vote may be the very thing which pushes those not in that category to vote the other way.
It was clear that Gerry Adams was in that category. The belief that he was an IRA leader at a point when some of the worst atrocities were carried out by that organisation meant that he was a hate figure for unionists.
In choosing to replace him with a southern leader who had no IRA background, Sinn Féin might have thought that it had moved significantly to address that issue.
But the events of the last week suggest that the issue is with the party rather than simply its leader.
On Saturday, Mary Lou McDonald walked behind a banner saying ‘England get out of Ireland’ while taking part in New York’s St Patrick’s Day parade. That fact was not reported as a result of a journalist happening to picture the Sinn Féin leader or a member of the public snapping her beside the slogan. Rather, a picture of Ms McDonald behind the banner was posted on Twitter by Sinn Féin’s official account along with the words ‘No explanation needed’.
Evidently, the Sinn Féin press officer who posted the photo thought that this was a positive piece of political propaganda.
In some ways, it is far from the worst gaffe by a political party. The scale of the reaction has surprised many people – and plenty of unionists, because they always assumed that Sinn Féin endorsed the sort of crude ‘Brits out’ mantra on the banner.
Indeed, for many people what the banner endorsed was far less objectionable than Sinn Féin’s continued belief that the Provisional IRA was right to set off bombs which blew apart innocent men, women and children of all faiths and none, and of all political persuasions.
The real political damage wrought by Ms McDonald has been with those who were willing to give Sinn Féin’s new leader the benefit of the doubt or who have been moving to more seriously consider Irish unity.
Three of those (albeit one is a direct political opponent, Colum Eastwood) who spoke at the recent uniting Ireland conference in the Waterfront Hall rapidly came out to denounce what Ms McDonald had done.
Terry Wright, one of the most moderate unionist voices in Northern Ireland, was similarly dismayed by what he saw. The former UUP deputy chairman – who quit in 2013 over the party’s closeness to the DUP – had last month organised a high profile invitation for Ms McDonald to address a large group of ‘civic unionists’ at Queen’s University.
This week he said that Ms McDonald’s support for the sentiment on the banner was contrary to her stated vision for a ‘new Ireland’ of equals and questioned whether her inclusive words last month were “expedient rhetoric designed to mask strategic and political intentions that are worrying in their implications”.
Tone-deaf to the reaction, Sinn Fein’s immediate response was to dismiss the widespread criticism as “faux outrage”.
Whether explicitly or implicitly, at the heart of most of the criticism of the banner’s slogan was the fear that it implied that partition was somehow an English problem.
At best, that betrayed ignorance of the agreement to which Sinn Féin subscribed in 1998 - that it is for the people of the island of Ireland alone to decide whether partition continues - and at worst it was some sort of dog-whistle of endorsement to a sectarian philosophy which uses ‘England’ as a euphemism for unionists.
Sinn Féin insist that is not the case, and the likelihood is that this was a gaffe by a southern leader who failed to comprehend the significance of the banner.
The party is unlikely to lose many, if any, votes over the row. If anything, that incentivises this sort of behaviour - for both unionists and nationalists - because it reaps electoral rewards.
But that reinforces The Farage Paradox. Sinn Féin’s nous for electoral politics could here be at the expense of its grand goal of Irish unity, which will involve persuading those who now don’t support Irish unity
If unionism and nationalism are serious about winning a border poll, they will be strategically reaching beyond those whose referendum votes are already in the bag.
For all the talk, at this point the evidence suggests that both the DUP and Sinn Féin are still largely concentrating on electoral politics.
If a border poll is held while Mary Lou McDonald is Sinn Féin’s leader, will the official unity campaign view her as its key asset – or be attempting to keep her canvassing republican heartlands and away from the media?