On May 18, 1998, one of the most iconic images of the past 25 years in the north of Ireland was created as John Hume and David Trimble stood onstage in Belfast at either side of U2's Bono. The Good Friday Agreement had been signed one month earlier and the jubilant atmosphere at the concert was evident as the three smiling figures stood holding hands which were raised to the sky. The air was tinged with hope that the agreement would be endorsed by the people in referenda three days later, which it was in the north by 71%.
Hume's thinking since the 1970s underpinned much of the agreement and the SDLP entered the negotiations as the largest representative of the nationalist community. Amid the current reigning duopoly of the DUP and Sinn Fein, some may forget that the SDLP was nationalist top dog until 2001. It is with a certain irony that only three years after arguably the party's greatest achievement since its inception in 1970 it was electorally surpassed by its nationalist rival.
Why did the SDLP electorally decline in the immediate post-agreement period, rather than reap the anticipated electoral dividends? This was the question I was pursuing when I first met John Hume in his Derry home 17 years ago.
Much had been written on the rise of Sinn Fein, but I wanted to delve into the mind of John Hume regarding the decline of the party which he had led from 1979 to 2001, during which time he acquired the accolade of Northern Ireland statesman.
The Irish playwright George Bernard Shaw said that "a gentleman is one who puts more into the world that he takes out"; a sentiment that could be written about John Hume.
Testament to his character, he insisted on proceeding with the interview to help a student despite being ill. It is also a testament to Hume's practicality and wit (and school teacher background) that he asked to see my handwritten notes. I gladly obliged and, when he glanced down them, he pointed to the word "consociationalism" (a term favoured by academics to denote power-sharing) and said, "That's not a word."
For some commentators, the SDLP had achieved its ultimate goal with the agreement and power-sharing and, therefore, electoral decline was inevitable against the organisationally robust, all-Ireland, grassroots-orientated Sinn Fein.
But Hume believed that, as a social democratic party, the SDLP had a key role to play in post-agreement politics: "Working to break down traditional barriers, because once the institutions of the Good Friday Agreement are in place and the representatives of all sections of the people start working together and spilling their sweat, as I say, and not their blood, then the barriers of the past will be eroded and a new Ireland will evolve in a generation or two. The SDLP will play a major role in that, because it will be down to real politics."
The party had a good result last December in the Westminster elections, when Colum Eastwood and Claire Hanna topped the polls in Foyle and South Belfast respectively and it remains to be seen if the party can build on that momentum. But the SDLP has largely failed to regain lost ground.
Its decline could be attributed to factors including organisational deficiencies, or possessing a more "mixed" identity than Sinn Fein; a legacy of having been founded around a number of individuals such as Hume, Ivan Cooper and Paddy Devlin.
In fact, at the party's first meeting, when a name was being decided, the different strands of political tradition were evident when the more labour-orientated individuals wanted "labour" to go first in the party's name before social democratic. (That is until they realised they would be the LSD party.) Others, including Seamus Mallon, attributed the SDLP's eclipse to the primacy of Sinn Fein in political negotiations with the British and Irish governments.
Once Sinn Fein came into the process it was inevitable that the party would occupy a central role in any negotiations around an IRA ceasefire, or decommissioning, thus leaving the SDLP on the sidelines.
Hume's engagement with Gerry Adams through the Hume-Adams dialogue (1988-1993) drew criticism from some quarters, including from within his own party, as a narrative developed that Hume sacrificed the SDLP to bring Sinn Fein into the process.
The reality, of course, is a much more complex, nuanced picture than that, but I wanted to get Hume's take on this personal criticism.
He responded: "Well, I thought it was the duty of everyone to do everything they could to get peace on our streets. My objective in talking to Gerry Adams was to get a complete end to violence and get all parties involved."
Hume rejected the traditional republican position that consent was tantamount to a unionist veto. Central to his message was the need to unite the people of Ireland, rather than unite territory.
An SDLP letter to Sinn Fein in July 1988 stated: "It is people who have rights, not pieces of territory, and it is the Irish people who have the right to self-determination."
Hume's argument that Irish unity needed to be achieved by consent of the people became the principle of consent (in the north), which is central to the Good Friday Agreement. For many, his legacy will be defined by the acceptance of this principle by Sinn Fein, a cornerstone of the peace process.
As the message of Sinn Fein moved closer to that of the SDLP and the IRA campaign had ended, the nationalist electorate opted for what it viewed as the "greener", more robust, representative of their interests.
That October day in Derry, as I interviewed Hume in his home, there was a key point which he wanted to get across and that was the constancy of the SDLP message over 30 years. Dubbed "Humespeak", it was a message which ultimately prevailed through the Good Friday Agreement.
Hume eagerly pointed out: "When you look at the SDLP's policies since its very foundation, we have been very consistent in our analysis of the problem; the three sets of relationships (within Northern Ireland, north-south and east-west).
"The problem hadn't changed, therefore neither did our approach to solving it. When you look at the Good Friday Agreement, you're looking at what the SDLP has promoted throughout 30 years."
Fourteen months later, at the SDLP conference in Belfast in 2005, I watched John Hume take to the stage to address those assembled, including Gerry Conlon of the Guilford Four, who had said from the platform, "This really is a party who cares about the individual."
In assessing the diminished position which the SDLP found itself in, despite its significant achievements, Hume told delegates: "Overcoming difficulties is what we have done well." The party's problem was that "we haven't boasted enough about it".
Dr Marisa McGlinchey is Assistant Professor at Coventry University's Centre for Trust, Peace and Social Relations. Her forthcoming book on the SDLP will be published by Manchester University Press