The release of political prisoners is the single most potent argument that paramilitaries use in favour of the peace process; it is also the most difficult element democrats have to accept.
Recently, it threatened to sunder the loose alliance of republican paramilitaries opposed to the agreement - the "Real IRA", the Continuity Army Council and the Irish National Liberation Army - as the INLA signalled it was preparing for an autumn ceasefire in order to secure the release of its prisoners.
On both sides of the Border, policemen and the bereaved have objected to the release of prisoners found guilty of murder. And the DUP and the UKUP have used the release of paramilitary prisoners and the sharing of power with Sinn Fein as their main criticisms of the agreement.
Responsibility for the Omagh bombing has been laid at the door of the so-called "Real IRA", a splinter group of dissident Provisionals, because of the codeword used in the inaccurate warning that was given. The slaughter of civilians was clearly designed to place all dissident groups outside the terms of the peace process and to ensure a continuation of the armed struggle.
What better way to convulse Northern Ireland, undermine the loyalist ceasefires and prevent the prisoner release system being extended to the INLA and others than through an atrocity of the kind that occurred at Omagh on Saturday? What politician would argue for the extension of the scheme following the massacre of so many innocent civilians? It would be difficult enough to hold the line on the commitments already made.
The Taoiseach recognised the tactic underlying the bombing. And he indicated there would be no turning back from the terms of the Belfast Agreement. Following a meeting of the Government's security committee in Dublin, Mr Ahern appealed to the INLA and the Continuity Army Council to declare an immediate, unequivocal ceasefire.
The governments were united in their determination to bring peace to Northern Ireland and make the agreement work, he said. New security measures would be adopted and they would crush the dissident republican elements that had worked since last autumn to wreck any agreement that emerged. In an oblique reference to the "Real IRA", he said: "We cannot let 100 people or less succeed in doing this . . . we have to be ruthless."
Recognising the newly-established "Real IRA" would not be swayed by early prisoner releases, Mr Ahern concentrated pressure on those organisations with a significant number of prisoners. Leaving nobody in any doubt that the Government would respond aggressively to the massacre, he offered a last chance for the INLA and the Continuity Army Council to benefit from the terms of the agreement.
Normally, he said, such organisations went to ground following an atrocity. But this time he appealed to them to declare an immediate cessation of violence "because we have to take this into account when we move to crush this campaign and we will do that".
The Taoiseach stopped short of promising the introduction of internment to deal with the situation. But the full rigours of the Offences Against the State Act will be utilised. And legislation may be required. The precise nature of the Government's response will not be decided until next Wednesday's special Cabinet meeting. And, even then, action by the security forces is likely to come before any official announcement.
Opposition Dail parties are likely to endorse any action proposed by the Government. In that regard, the Fine Gael leader, Mr John Bruton, called for an all-Ireland security initiative and said those responsible for the bombing were addicted to violence and had no place in a civilised society.
The President, Mrs McAleese, visited Omagh and described those responsible for the massacre as "serial killers".
Sinn Fein's response was particularly significant. The president of that organisation, Mr Gerry Adams, condemned the bombing unequivocally and called on those responsible to abandon violence before going on to meet the British Prime Minister, Mr Tony Blair. He emphasised the need to make political progress within the new Northern Ireland Assembly and later discussed likely developments with the Taoiseach.
Mr Martin McGuinness spoke of the need for Sinn Fein to hold its nerve and to lead from the front in supporting the Belfast Agreement. By doing that, he said, it could convince dissident elements that their actions were futile.
From within the unionist community, the DUP leader, the Rev Ian Paisley, used the bombing to attack the agreement, the release of prisoners and the appeasement of republicans. The governments, he said, were guilty - "the blood is as much on their shoulders as on the people who laid the bomb".
As the full horror of the atrocity became clear, Ministers cut short their holidays. The Taoiseach returned from Kerry; the Minister for Justice, Mr O'Donoghue, from the Canaries; and the Tanaiste, Ms Harney, flies back from Portugal this morning.
Mr O'Donoghue was briefed on developments by the Garda Commissioner, Mr Pat Byrne, at Dublin Airport last night. Both men will travel North today to meet the Northern Secretary, Dr Mo Mowlam, and the RUC Chief Constable, Mr Ronnie Flanagan. They will exchange intelligence information on the dissident group concerned and co-ordinate the actions of the police forces in countering the threat they pose.
Following their meeting in Belfast, last night, Mr Ahern and Mr Blair emphasised the importance of continuing to consolidate the Belfast Agreement. It had been endorsed by people, North and South, and it had to be implemented. A small, fanatical, unrepresentative group could not be allowed to wreck the future of the people of Northern Ireland.