He often appeared distracted and, just last week, there were reports that he was not embracing the St Patrick’s Day visit to the White House with his usual energy and focus. While the decision was a surprise, taking a step back, there have been subtle signposts for many months.

Mr Varadkar has been on the national political stage for 17 years. A politician of enormous intellect, he showed early promise when he was first elected in 2007 and he emerged as a straight-talking and ambitious high-flyer. He served a short political apprenticeship in the Fine Gael backbenches, before being appointed to Cabinet by Enda Kenny in 2011.

Mr Varadkar’s performances as a minister are mixed, his early terms in transport and health were severely constrained by the economic crisis, and he was ill-suited ideologically to social protection. However, he developed a reputation for policy competence, ability, and strong communication skills.

His keen political nous and organisational skills were showcased when he triumphed, almost on the first morning, at the 2017 Fine Gael leadership election. Mr Varadkar comfortably defeated Simon Coveney and was elected as Taoiseach on June 27, 2017.

Leaders of major parties can be evaluated in three broad areas: In public office (Taoiseach), as managers of their parties’ interests and operations, and as campaigners. Leo Varadkar gets a mixed report card. He has some highly significant achievements as Taoiseach, and he listed several in his resignation speech.

There is no denying Varadkar’s careful stewardship of the State through the most challenging early period of the pandemic.

His profile as an international statesman was earned through his confident and creative leadership on Brexit, the generosity of the Irish response in welcoming 100,000 Ukrainian citizens to Ireland after the Russian invasion, and in his advocacy for the plight of the Palestinian people.

In his last week as Taoiseach, he brought uncomfortable truths to the American political elite about their enabling of atrocity in Gaza. It is a difficult thing to highlight unpopular truth to a friend and ally, all the more so when that state is the most powerful in the world.

However, there are also grave problems that endured throughout his premiership — most notably the housing crisis. The acute shortage of houses will persist for another decade, and its legacy will have pronounced impacts for generations.

As a manager of his party, Mr Varadkar developed a reputation for being available to speak with colleagues at all levels. He had an inclusive approach to party management and he carried out important groundwork on candidate selection, including attracting more female candidates.

He was an engaged party manager, but he leaves a troubling vista behind, with one third of incumbent TDs not seeking re-election.

While he may have created a slim lifeline for the next party leader to reposition the party and reconnect with voters, the fact that he has taken the decision just two months before important elections creates a near-impossible challenge for his successor.

And that leaves his final function as party leader, that of chief election campaigner for Fine Gael. It was expectations about his electoral abilities that led to his resounding selection as party leader, and it is here that his reputation is weakest. Fine Gael secured modest gains at the local and European Parliament elections in 2019, but the party had a dreadful general election in 2020.

Varadkar’s popularity soared after the election because of his excellent pandemic leadership, and the party was eventually returned to Government.

Fine Gael and Mr Varadkar were saved a technicolour dissection of the party’s electoral problems, but the issues mounted in the background.

After more than a decade in power, the party looks tired and it lacks a coherent policy platform that is partially fed by Mr Varadkar’s own image-reality dichotomy. Mr Varadkar was loudly criticised from the left as a Thatcherite right-winger. He often fed this with his own rhetoric, but the reality of Mr Varadkar in power was of a “middle of the road” social democrat.

Promises of tax cuts, pro-business policy, and an assault on red tape were drowned out as the Government oversaw soaring public spending, massive increases in the social protection budget, and valuable improvements in workers’ rights. Left-wing critics were never persuaded by the social democratic turn of recent governments, and centre-right Fine Gael supporters were left disappointed. The problems have amplified since covid and are now sitting in the in-tray of the incoming leader.

Perhaps the most damming evidence of Fine Gael floundering is found in the idea that there might not be a contest to become the next party leader and Taoiseach.

That the leadership of Fine Gael is not something worth competing for highlights the political fatigue that besets the party.

Seeking a fourth term in office is an enormous hurdle for any party, but the world-weariness and lack of enthusiasm must, at least partly, be laid at the door of Mr Varadkar.

Nevertheless, he departs the political stage leaving Ireland a prosperous and liberal state in an increasingly uncertain world.

• Theresa Reidy is a political scientist at University College Cork