The US did not make the Good Friday Agreement, but it is difficult to think of agreement being reached without the United States, then or now.

From the tireless efforts of Senator George Mitchell – the first US special envoy to Northern Ireland, who chaired the multiparty talks that resulted in the agreement – through a series of successors right down to the newest arrival, former Congressman Joe Kennedy III, the United States had supplied a diligent honest broker to whom all the parties could appeal for help in overcoming seemingly intractable disputes.

Mr Kennedy's role as Economic Special Envoy pointed to the latest phase of US involvement, laying a heavier emphasis on prosperity in the years ahead as a reason for Northern Ireland’s politicians to work together.

Peace and prosperity are of course linked, and the US administration is offering assistance to encourage private sector investment in Northern Ireland, as further support in deepening and developing the role of parliamentary politics in Northern Ireland.

And of course there was the top-level political support, from presidents Clinton, Bush, Obama, Trump and Biden – hands on and hands off, as needed.

Bill Clinton and George Mitchell in the White House

An astonishing amount of political capital poured from the mightiest super-power into a very small speck on the map of this earth. Why did it do so – and will it continue with this incredible level of support?

Mr Clinton’s role was pivotal – from his appointment of George Mitchell as special envoy and later chair of the peace talks, to his decision to grant a visa to then Sinn Féin leader Gerry Adams to visit the United States and address supporters there – an event seen as a key breakthrough in moving the IRA away from violence and towards politics.

Writing in the Financial Times at the weekend, Charles Powell, a former UK civil servant who was Tony Blair’s right-hand man in the talks process, reflected on his time at the US Embassy in Washington in the early to mid 1990s – where he had to lobby the Clinton administration against giving the visa to Mr Adams.

"In retrospect, the president was right; the visa allowed Mr Adams to convince the hard men on the IRA’s army council there could be political progress," he wrote.

In a Washington Post article at the weekend, Mr Clinton himself reflected on the agreement and its power of endurance, which he attributed to the way the agreement was made – by the people and their representatives, from the ground up – not imposed from above.

"The process was driven by the people," he wrote. "They had grown weary of the killing and the arbitrary tragedies of non-lethal political violence, and weary of the economic deprivation borne of the divisions."

He said the people wanted the violence to end, and that desire for peace had kept the agreement going through rough spots over the past quarter century.

The most recent of these was Brexit and the political dislocation around the Northern Ireland Protocol – an attempt to mitigate the border problems of the UK’s withdrawal from the agreement that had gotten rid of the economic border across the island of Ireland – the Single European Act.

At an event in New York last week organised by the Friends of Sinn Féin, Mr Clinton threw his weight behind the Windsor Framework, the agreement between the EU and UK to streamline the workings of the protocol.

"Brexit was a roadblock. It threatened to blow up the whole thing. This Windsor agreement I think is about as good as anybody could get. And now politicians can get on with the peoples’ business. People voted for delegates to serve in the Northern Ireland Parliament in Stormont," he said, to sustained applause from the crowd at Cooper Union university’s great hall.

The Brexit fallout had been the cause of the most recent US political intervention, that of the Biden administration, which has quietly pushed the UK to reach an agreement with the EU.

That pushing became particularly urgent after the invasion of Ukraine, as the US did not want the issue poisoning the already poor relationship between the EU and UK – it wanted both parties to concentrate on the Russia question.

Britain had stepped up their efforts to lobby Washington to pressure the EU but got little traction – not just with the administration but with Congress also (important for trade deals in particular).

The House of Representatives Committee on Ways and Means was forthright in stating there would be no trade deal with the UK if the Good Friday agreement was endangered in any way.

This message was further emphasised in St Patrick’s week by the leader of the majority faction in the US Senate, Chuck Schumer, who told the Ireland Funds Gala where he was honoured (along with the House of Representatives Speaker Kevin McCarthy), that the Senate would veto any trade deal with Britain if the Good Friday Agreement was threatened.

The former chair of the Ways and Means Committee, Representative Richard Neal, marked the 25th anniversary this week saying: "As a guarantor of the agreement, the US has the indispensable role of continuing to uphold the principles embodied in the peace accord, ensuring no return to a hard border.

"The gains of this agreement have brought peace to the island of Ireland for 25 years, and we must continue our work to protect and strengthen these gains for future generations to enjoy."

Richard Neal said a devolved government 'has to work'

Looking to the future is a key theme of US involvement now. US politicians – even those intimately involved at the time – have little sentiment for past glories. They want results today, and into the future. In particular they want to see the institutions set up by the Good Friday Agreement fully operational.

The non-existence of the Assembly and Executive at Stormont is glaringly obvious by its absence from the itinerary of President Biden’s trip to Northern Ireland this week.

It would have been the obvious place for him to make an address to celebrate 25 years of political progress.

"I think that the devolved government has to work. And it doesn't work in its present form. And something has to be done so people can’t veto its ability to govern," said former Congressman Bruce Morrison, one of the most influential figures in persuading the US to support the Irish peace process, and move the IRA away from violence.

He reflected on the unique power of the US to bring about change.

"I think we are a place that all the participants look to for some support," he said. "I think we need to be there for support - not to dictate what should happen, but to say, we've got people's back.

"What we mean by that is, we want peace and prosperity for people who live in Northern Ireland. We want them to have a real choice about their future, constitutionally, economically, in every way. And we believe in a democratic process to get there. So we're important because we believe those things."

The now former Congressman pushed hard to get his old law school friend, Mr Clinton involved in the nascent Irish peace process back in the early 90s, when Mr Clinton was starting his run for the White House.

The prize was stopping the violence and re-establishing the primacy of politics.

"I'm very pleased that the Troubles are over. And I think there's no going back. I think that's real progress and wouldn't necessarily have been predicted 25 years ago. On the other hand, the politics are very divisive, but I think that there's a grassroots movement toward more accommodation.

"That is not necessarily reflected in electoral politics. I hope it will be and I think making adjustments in Stormont so that people can't keep it from functioning are necessary. So that voters think that they're voting for a real thing, not for a talk shop," said Mr Morrison.

Ambassador Mitchell Reiss knows how difficult it can be getting the institutions back in operation after a breakdown.

He was the special envoy to Northern Ireland from 2003 to 2007, appointed by President Bush to try to get power-sharing government restarted after the Ulster Unionist Party left the government over the IRA’s refusal to decommission its weapons. That shutdown lasted from 2002 to 2007.

Mitchell Reiss said there is 'much more work to be done'

"Well, first of all, there has been remarkable progress in 25 years, so that needs to be stated. upfront. There's clearly more work to be done in terms of having a consistent political representation, so that the people have a voice and that Stormont is up and working.

"You also, I think, need to tackle the paramilitary influence and control it exerts over its communities. There's more progress needed in socio-economic deprivation in certain areas. And education I think is another area that could also be addressed. So great progress, but much more work to be done."

But nothing insurmountable - or nothing presenting the kind of challenge that there was 25 years ago in putting an end to straight up violence?

"No, I think that's exactly right. I think if you look at the mountain that was climbed 25 years ago, and all the efforts that that took, it's really quite remarkable. These are also challenges but they're challenges that Northern Ireland has in common with many other places.

"And so there's some best practices that can be used, and again, I think it's a question of political willpower. Getting the formula right for Stormont, I think is absolutely crucial," he said.

Senator Chris Murphy of Connecticut is part of the current generation of US politicians, one who takes a particular interest in Ireland and is close to the Biden administration.

"This is a moment to celebrate what this agreement has meant and America's small role in it, but also make sure that we continue to stay active to make sure that that piece is preserved for the next generation."

Of course, the United State’s role was not a small one, and it has had to get actively involved once again because of Brexit and the falling out over the protocol.

Senator Chris Murphy said 'both sides' of US politics support the Good Friday Agreement

How difficult was it to motivate the American political machine to put its weight behind this issue?

"There certainly is a division in the United States around opinions on Brexit. But there's no division to the United States when it comes to the Good Friday Agreement.

"We've been able to keep bipartisan support in the Senate and in the House around everything necessary to prioritise the preservation of the Good Friday Agreement and notwithstanding differences we may have on whether Britain should stay or leave the European Union.

"This agreement, you know, is rooted in support both sides, the Democratic and Republican divide here," said Senator Murphy.

Mr Clinton in his New York speech talked of the power of the example of the Good Friday Agreement in efforts to broker peace deals in Kosovo and Colombia.

But for Mr Murphy, the agreement also has power as an example within the US itself:

"A lot of current American politicians came of age when the definition of American power was the Iraq war in the Afghanistan war.

"And so it's really important to celebrate these moments when the United States led diplomatic breakthroughs that led to significant eras of peace and so I think especially now, when we saw this collective hangover in the United States from decades of war, and American foreign policy being defined by war, it's especially important now that we celebrate and remember these moments where America led important diplomatic agreements."