Phil Hogan's resignation is a very dramatic development, marking a decisive moment in one of the most fractious periods in Irish politics.

It is almost unprecedented for a European Commissioner to resign. He has held one of the most important European portfolios at a time when international trade has been at the forefront of historic upheavals in global politics, from Brexit to trade wars with the United States and China, and even how the Covid-19 pandemic could change the way trade operates.

But it was that very pandemic which caused his downfall. His defensive, then fragmented response to the Clifden golf dinner raised the hackles of many Irish people angered at what were seen as double standards, and dismayed the coalition government, which feared that the critical message on curtailing infections was being drowned out by the crescendo of public anger over the controversy.

Phil Hogan did apologise, at times profusely, first in a statement, and then during an RTÉ News interview. But his position was damaged further by his defence that a negative Covid-19 test absolved him of the 14-day period of restricted movements. Official statements suggested otherwise.

Despite a passionate appeal for forgiveness and to be able continue his work as trade commissioner, the Government still could not express full confidence in him, and this put Dublin on a potential collision course with the European Commission.

That collision has been averted. Phil Hogan has chosen to resign himself.

Commission President Ursula von der Leyen issued a brief statement, respecting his decision and thanking him for his "tireless" work as a trade commissioner and for his time as agriculture commissioner.

Hogan insists the decision to resign was his alone. He told Ms von der Leyen in the middle of yesterday afternoon that he was tendering his resignation. Certainly the pressure from Ireland was relentless. He may have felt shielded by the treaty-based independence of the European Commission and a deeply held institutional view that commissioners cannot be at the mercy of partisan national politics.

But at a certain point he must have realised that his credibility and that of the Commission was starting to wither under the heat of public and political odium. He had largely been cast adrift by the Government. It’s understood the discrepancies over his Covid-19 test result were the element which finally forced his hand.

Critics will say this was entirely his own creation and that a more contrite response and detailed explanation of all of his movements from the outset could have drawn the poison out of the debate. Had he said he had made an honest mistake in believing that a negative Covid test exempted him from his obligations he may well have been given the benefit of the doubt.

But that is easy hindsight. More than many Irish politicians, Phil Hogan is a lightening rod for public anger, a legacy of his handling of water charges. And yet, when he was confirmed as trade commissioner there was glee in Irish social media that this blunt speaking and physically imposing Irishman, with a long record of taunting Brexiteers, would be the perfect foil for Boris Johnson.

In the event, the negotiations did not pan out like that, and that was a caricature Hogan himself did not envisage. Yet those who defended him in recent days said it was in the national interest that his role in the Brexit negotiations must trump political anger over his allegedly egregious wanderings from one county to the next.

His role in Brexit can neither be overstated nor understated. Michel Barnier remains the frontline negotiator, but he and Hogan have been close confidants, and no-one should underestimate the role Hogan played in ensuring that the Irish border dilemma was understood in Brussels and that the interests of one small country on the periphery of Europe were protected to the very end.

It was Hogan who ensured that Ireland understood that its border concerns needed to be outsourced to Brussel and Barnier’s Article 50 Taskforce. Until his intervention in an Irish Times op-ed in January 2017, some in Dublin believed the issue could be resolved bilaterally with the UK.

Hogan headed up the powerful Directorate General for Trade. Scores of his staff have been deployed in the future relationship negotiations with the UK, meaning he had a wealth of expertise on hand. Diplomats say he also had close contacts in London, and acted as a conduit for officials on both side when necessary.

It is by no means certain Ireland will hold on to the trade portfolio. There is no evidence that Hogan’s resignation was part of careful choreography in which the Commission would be relieved of the ongoing agony and Ireland would keep trade.

One name that has surfaced in recent days is David O’Sullivan, a former secretary general of DG TRADE, the one-time top civil servant to former commission president Romano Prodi, and an EU ambassador to Washington. He has years of institutional experience and is grounded in global trade, but he might not be the kind of political figure that governments like to nominate to the Commission.

Enda Kenny, the former taoiseach, could consider running, as could Andrew McDowell, Kenny’s one time chief economic adviser, who is just finishing a four-year term as vice president of the European Investment Bank (EIB).

Ireland may well be the beneficiary of Hogan’s decision to quit. A potential constitutional crisis has been averted, and the State can quickly move to steady the relationship with Brussels. Micheál Martin’s careful assertion of the Commission’s independence will have been noted.

Having laboured over the composition of her College of Commissioners last autumn, Ursula von der Leyen was significantly put out by Hogan’s bid to leave Brussels and take up the job as director general of the WTO. Under pressure, Hogan dropped his bid and the president was spared the pain of a politically hazardous reshuffle, given how prized his portfolio is to the larger member states.

However, there are ominous signs that Ireland will not carry on with trade. The Commission is only into the first year of its mandate. Had there just been six months left then keeping an Irish person in trade would have been an easy choice for a caretaker president.

Von der Leyen will want someone who can take on a very ambitious trade agenda that will run for four years and beyond. One source has pointed out that countries do not "own" portfolios. For Von der Leyen, Hogan was the right fit at the right time. He had a successful term as agriculture commissioner, cutting his teeth on trade by way of the Mercosur negotiation.

She will want his replacement to have the same heft, expertise and experience, not necessarily the same accent.

The next steps are as follows: Ireland will have to nominate a number of candidates (Von der Leyen has asked countries to propose at least two, one male and one female). She will pick a candidate and then allocate a portfolio which she believes will suit that candidate, and will contact the European Parliament for a hearing to take place.

For Phil Hogan, his mandate as trade commissioner ended the moment he resigned. There is no caretaker role. Another commissioner will be allocated his portfolio and he will have to vacate the European Commission headquarters as soon as possible.

It is a brutal end to an illustrious career, throughout which controversy and brutal politics sometimes lingered like low morning mist. It is a major setback for the European Commission, to lose a commissioner at such a time, so early in the mandate. Many observers in Europe cannot quite believe how a golf dinner in Clifden exploded in so many people’s faces and culminated in Ireland cold shouldering its man in Brussels, and potentially losing a highly coveted portfolio.

In Brussels officials watched the debate in Ireland and could see it was entirely one-sided. One senior official noted there was hardly a single article supporting Hogan. Would this have happened in another member state if politicians had been found to have breached the rules? A hard question to answer.