There is only one duty that really counts in statesmanship - the duty to get the crucial calls right. Notwithstanding the considerable record of achievement of former British prime minister Tony Blair's governments, his leadership is now widely regarded as having been a failure.
This is largely because of one ruinous error: his agreement to UK participation in US president George W Bush's disastrous 2003 invasion of Iraq. In the 1960s, another Labour premier Harold Wilson, in contrast, escaped history's condemnation by refusing to allow the UK to be dragged into the growing quagmire of Vietnam by then US president Lyndon B Johnson.
As for David Cameron, it is likely nothing will be remembered of him a generation from now beyond one calamitous misjudgement: his decision to hold the Brexit referendum.
What will future generations make of Taoiseach Leo Varadkar's decision to go for broke on the issue of a frictionless border with Northern Ireland?
My first encounter with this policy occurred when I attended the third plenary session of the All-Island Civic Dialogue on Brexit in Kilmainham in September 2017, where Varadkar expounded the Government's unequivocal position that there could be no re-introduction of a border in Ireland. Nominally the confirmation of an existing government position, Varadkar's speech was, in reality, the first explicit declaration of such a hardline stance. I was rooted to the spot on hearing it.
The various good grounds for fighting for a frictionless border were certainly clear. They included (a) avoiding creating border-post targets for terrorism; (b) avoiding undermining nationalist feelings and thereby destroying a key foundation of Northern Irish peace; and (c) avoiding destroying blossoming cross-border economic activity. But I, like others, thought that holding off a hard border nonetheless politically impossible. Ireland would simply have to accept a reconstituted hard border as a fait accompli and content itself with seeking to assign blame where it belonged - with a UK Government which, despite contrary rhetoric, has always prioritised a hard Brexit over any consequent risks to peace in Northern Ireland
Varadkar evidently thought otherwise. Yet the risks involved in his decision to insist on no border controls were and are enormous. It is no exaggeration to call this the greatest gamble in recent Irish political history.
If a friction-free border remains, the benefits are clear. If it fails, two things happen.
Firstly, particular sectors of the Irish economy will suffer hugely (and with potentially more than merely economic implications). Farmers, the food industry, small and medium-sized enterprises and border enterprises - all focused on the UK market - will be dealt a savage blow. Ironically, Ireland, which exports virtually everything it produces, will be economically affected far worse than the UK, a much larger economy which, as one would expect, trades more with itself than Ireland does.
Secondly, Ireland will end up with the very thing it has sought to avoid - a hard border, since this will be legally required of Ireland under European Union law, and of both the UK and Ireland under WTO law.
Varadkar's demand initially seemed unlikely to succeed. The prerequisites to its success were considerable. It would require that Northern Ireland, either alone or with the UK as a whole, stay in a customs union with the EU, and retain elements of the single market. (Any other result implied a hard border).
Rather like the Grand Old Duke of York marching up to the top of the hill, it seemed Varadkar would end up marching his metaphorical troops back down again on this issue. Too many diplomatic battles had to be won - the EU would have to back the position, then other EU states would have to back it, then the British Government would have to accept it and finally the UK parliament would have to ratify it.
Yet in the event, hill after hill was taken. The EU and its Brexit negotiation team led by Michel Barnier - backed up by European Commission President Jean-Claude Juncker and European Council President Donald Tusk - supported Ireland to the hilt against the departing UK's government, and remarkably the support of the other 26 remaining states - some of whom are risking hefty trading relationships - has largely held together.
British prime minister Theresa May, having first declared that what is now the backstop involved compromises no UK government could accept, subsequently agreed to it (albeit with a supposedly temporary customs arrangement having been broadened from a Northern Irish arrangement to a UK-wide one - a remarkable concession from the EU).
Up to this point, it was largely so far, so good for the frictionless border - but the last hill remains to be taken: UK parliamentary approval of some means of guaranteeing a frictionless Northern Ireland border.
Defeat here will wipe out all previous diplomatic gains for Ireland. And the danger is huge. Under both UK and EU law, an economically disastrous (and hard-border-resurrecting) no-deal Brexit remains the default option. Ironically, a House of Commons majority opposes this economic self-harm. But such opposition counts for nothing, unless a Commons majority actively supports another proposal.
A considerable blow to frictionless-border hopes occurred with January 15's overwhelming Commons rejection of the EU-UK Brexit agreement. Absent this deal winning ultimate approval (still May's preferred option), then some other subsequently parliamentary-approved way of preserving a frictionless border must occur if a no-deal scenario is to be prevented (eg, a Labour victory in a general election followed by a soft Brexit, or a referendum reversal of the Brexit vote).
February 5 will see emergency legislation proposed by Labour MP Yvette Cooper voted on. This requires the UK government to delay Brexit, if no deal is approved by MPs by February 26. This proposal is inspiring real fears among hardline Tory Brexit supporters, who suspect - hopefully correctly - that delaying Brexit will see it abandoned, should a Labour government come to power or a second referendum take place.
For now, however, we still cannot tell whether Varadkar has met statesmanship's call, or simply brought an unnecessary economic catastrophe down on us all.
Gavin Barrett is a professor specialising in EU law at Sutherland Law School, UCD