Four years ago, at the height of the 2016 government formation talks, Enda Kenny made an offer that was unprecedented in its nature.

After seeing his party slump dramatically in that February's general election, the then Fine Gael leader and taoiseach was in trouble and needed help - any help - to cling onto power. 

So he turned to the most unlikely of sources.

His long-time political adversary, Fianna Fáil leader Micheál Martin, was the enemy at the gates of Government Buildings armed with his own plan for power.

But instead of manning the barricades with what limited resources he still had at his disposal, Mr Kenny did the unexpected, offered instead to share the keys to power, suggesting an historic rotating taoiseach role between the rivals for the next five years.

Until now, the moment in March 2016 was the closest Ireland has come to implementing a tag team taoiseach system which has been mooted since the early 1990s without ever being acted on.

If it sounded too good to be true to Fianna Fáil's leader, who despite a drastic upturn in fortunes was aware his party was still trailing Fine Gael 50-44 in Dáil seats, it's because it was.

Instead of grabbing the outstretched hand offering him the opportunity he had sought his entire political life, a suspicious Mr Martin slapped it away, believing an alternative confidence and supply deal from opposition gave him all the power while limiting the risk involved.

And just like that, the shared responsibility opportunity disappeared into thin air.

Until now, the moment in March 2016 was the closest Ireland has come to implementing a tag team taoiseach system which has been mooted since the early 1990s without ever being acted on.

But times change, and while in 2016 Mr Martin was uncomfortable with the prospect of sharing the taoiseach seat with his adversary, in 2020 he is humming a very different tune.

Due to the near three-way dead heat between Fine Gael, Fianna Fáil and Sinn Féin in the 2020 general election, over the past four months it has been almost impossible for a coherent government to be formed.

So, in order to avoid a second general election, both Mr Martin and Mr Kenny's replacement Taoiseach Leo Varadkar have returned to the 2016 back catalogue to dust down the rotating taoiseach plan and give it another go.

Should all three parties' grassroots members vote in favour of the deal, Mr Martin will be nominated taoiseach during a Dáil meeting most likely to take place on Saturday 27 June, and will take up the role immediately.

Publicly at least, Mr Martin and Mr Varadkar - who have made no secret of their mistrust of each other in the past - are suddenly the co-leaders of the potential Team Fine Gael-Fianna Fáil-Greens coalition.

And at the centre of that programme for government deal, which is currently being voted on by the parties, is the commitment for the Fine Gael and Fianna Fáil leaders to share the coveted taoiseach position evenly between them over the next five years.

What is a rotating taoiseach system and how will it work

In theory, the rotating taoiseach system is as simple as it gets.

If a government is formed in the coming week, Mr Martin and Mr Varadkar have agreed to share the taoiseach role as they will be the leaders of the two largest parties in the coalition, with 37 and 35 seats compared to Eamon Ryan's 12 seat Green Party haul.

Should all three parties' grassroots members vote in favour of the deal, Mr Martin will be nominated taoiseach during a Dáil meeting most likely to take place on Saturday 27 June, and will take up the role immediately.

He will continue in the position until 15 December 2022, just after the centenary of the Irish Free State's foundation, while Mr Varadkar will take up an increased tánaiste role which will see him given a specific office and greater say on economic matters.

As in the existing system, the taoiseach of the day will still be able to choose his cabinet, oversee 11 immediate appointments to the Seanad and lead the government as he sees fit.

When the first two and a half years of the government's at most five year term ends, the roles will be reversed.

And with that, both previous sworn enemies will - it is claimed - be presumably happy with their lot and content to live a political life of peace and harmony.

The Blair-Brown deal

Despite the seemingly simple plan, there are clear difficulties hidden just beneath the cosy surface.

And we don't have to look far from Irish shores to see the clearest example of what can occur when those difficulties veer into view if handover gentleman's agreements go wrong.

After the tragic death of John Smith in 1994, the British Labour Party needed a new leader. And, luckily, they had two ready-made candidates from which to choose.

Tony Blair and Gordon Brown were the two up and coming stars of their party, and were destined to contest a race which risked dividing their colleagues.

Despite popular opinion in recent weeks, the concept of a shared leadership role is not unheard of in this country. In fact, before the 2020 political quagmire, it had already been mooted on three occasions over the past 30 years

So before that happened, they agreed to a more mature solution.

Mr Blair would be allowed to seek the leadership uncontested, and if he became prime minister in 1997 would only serve two terms before handing the reigns of power over to his colleague Mr Brown.

The smiling Mr Blair agreed to the deal. 

Only, once the first stage was over, he had a sudden change of heart, with Mr Brown being left frustrated and blocked from real power when his prime minister decided he would much rather not step aside, if you don't mind, in 2005.

While Mr Blair eventually stepped down two years later, in June 2007 - helpfully handing power to his colleague just as a worldwide recession was looming on the horizon - the delay caused bitter acrimony between the pair which has since been immortalised in the political TV drama The Deal.

And although the Irish Martin-Varadkar conundrum has sought to side-step any such difficulties by ensuring the rotation plan is clearly outlined in black and white in the programme for government, the Blair-Brown dispute is a sign that when it comes to politics, gentleman's agreements are sometimes not worth the paper they are written on.

Ireland's own experiences of a pact

The British example is perhaps one of the main reasons why the idea of a rotating taoiseach has until now never gotten off the ground in Ireland.

Despite popular opinion in recent weeks, the concept of a shared leadership role is not unheard of in this country. In fact, before the 2020 political quagmire, it had already been mooted on three occasions over the past 30 years.

It's just it was always rejected or dismissed as being too fraught with barely hidden problems.

Former Labour leader Dick Spring was the first to suggest the idea during the 1992 general election, when the Spring Tide gave his party hope he may be able to wash a victor ashore, only for both Fianna Fáil's Albert Reynolds and Fine Gael's John Bruton to reject his advances.

Eventually, Mr Spring had to be content with the more traditional tánaiste role normally given to the leader of a smaller coalition partner as the then labelled two and a half party system continued.

A decade later, as the 2002 general election approached, rumours again appeared suggesting Ruairi Quinn - who by then had become Labour leader - could share the taoiseach role with Fine Gael's Michael Noonan, if they had enough seats to gain power.

The issue ultimately did not arise in part because Fine Gael dropped from 54 seats to just 31 and Labour from 21 to 20. 

In its best case scenario for both leaders, the deal will herald the end of civil war politics and the beginning of a long-awaited political peace, while giving both parties - and the country - the stability needed to govern.

But the hypothetical offer did not even make it as far as the poll booth, with Mr Noonan downplaying if not quite dismissing it during the campaign by saying he would accept "no pre-conditions" as to what would happen.

It was not until 2016 when the offer switched sides, with the hand of friendship reaching out from - not towards - Government Buildings when Enda Kenny suggested he and Mr Martin could jointly become taoiseach four years ago.

The Fianna Fáil leader rejected the idea at the time, and while circumstances change, it is worth considering why there is such a different view now.

The hidden pitfall: Can they trust each other?

Ultimately, the decision to seek a rotating taoiseach system and whether it will be feasible comes down to two key points: power and trust.

While it is understandable why both Mr Martin and Mr Varadkar have agreed to the potential deal, the harmony it is meant to bring is far from guaranteed.

In its best case scenario for both leaders, the deal will herald the end of civil war politics and the beginning of a long-awaited political peace, while giving both parties - and the country - the stability needed to govern.

But, just like with the Blair-Brown agreement, the plan is potentially littered with danger - whether accidental or designed - for the two politicians currently dominating the political agenda.

For Mr Varadkar, there is a significant built-in risk right from the start in that, should Mr Martin's Fianna Fáil improve in the polls come the would-be hand-over in December 2022, there is nothing stopping an election from being called at this time.

The programme for government deal is water tight and written in black and white, supposedly ensuring the hand over stipulation will be met.

Should Fianna Fáil and Fine Gael join forces, it will leave at least one of the parties vulnerable to an almost daily attack from Sinn Féin which will have free road as the main opposition party over the term of the next government

But events sometimes have a habit of occurring just when they are needed to bring down a government.

And with the halfway point handover scheduled for just after the expected third annual budget of the potential three party coalition, it is not outside the realms of possibility that a row would occur which would collapse the coalition just before Mr Varadkar is due to return.

Similarly, Mr Martin will be acutely aware that the deal may not be as beneficial to him, or at least his party, as it first appears.

While the Fianna Fáil leader is now - aged 59 and after spending most of his adult life as a TD - on the cusp of his biggest personal political achievement and seems set to avoid the faith of being his party's first leader not to become taoiseach, there were still reasons why he turned down a similar deal in 2016.

Should Fianna Fáil and Fine Gael join forces, it will leave at least one of the parties vulnerable to an almost daily attack from Sinn Féin - whose 37 seats from 42 candidates general election haul should not be forgotten - which will have free road as the main opposition party over the term of the next government.

In addition, it will leave Fianna Fáil and Fine Gael further open to the well-worn accusation that civil war politics or not they are - to its detractors at least - two sides of the same party.

In both instances, Fianna Fáil - which is currently far behind Fine Gael in the polls and is more likely than Fine Gael to face competition from Sinn Féin in its voter base - could be at risk.

And it means that, while the rotating taoiseach role is understandably enticing for both personal ambition and national stability reasons, the bed of roses in front of both leaders still may have some hidden thorns.

Four years on from Enda Kenny's offer of a rotating taoiseach being rejected, Fianna Fáil leader Mr Martin and Fine Gael leader Mr Varadkar are preparing to share the position they have fought over for so long.

The peace deal should either be taken at face value as a mature way to ensure political stability for the nation and their parties, or remind people of the old political adage that you only hug your enemy to know how wide to dig the grave.

But either way, a new chapter in Irish politics has just begun.