There is no doubt, after last weekend, about the bravery of Omagh's populace - or the extent of their tragedy; the terrible image of that burst water main coloured with gore and bearing severed limbs along the main street cannot be forgotten. It was the worst single-bomb atrocity since the Troubles began. But the question that is forming itself is: didn't we think that the Troubles were over?
The trouble with bombs is that it takes a single person to make one, and perhaps two to transport it, and another (or one of the three) to telephone a misleading warning - or not. There may be only about 100 people in the "Real IRA" or "Oglaigh na hEireann", but a high proportion of them are - or were - so-called "quartermasters" in the Provisional IRA, and thus know where the arms dumps are, how to get to them, and how to deploy the deadly material stockpiled therein. Speaking for Sinn Fein, effectively the voice of the mainline IRA, Gerry Adams and Martin McGuinness have denounced the Omagh horror; to the fury of many commentators in the Republic and elsewhere, they at first refused to be drawn further. This is because behind the question about the Troubles being "over" lies another: how far can the mainline IRA control the dissident groups? And what kind of support can the latter possibly have for a mindless war on random civilian targets?
"They're not normal," said a Kerry neighbour to me the day after the horror. Certainly not, but a clue to their self-referencing frame of mind comes from the Irish name chosen. "Oglaigh na hEireann" means "volunteers of Ireland", and is borrowed direct from the original republican paramilitary force set up before the First World War. In the view of the "Real IRA", theirs is the "normal" reality: they stand in the myopic tradition that refuses to admit that a formally partitioned Ireland has existed for several generations, and that all that has happened over the last 30 years has not eroded but solidified it.
One Sinn Fein spokesman, a supporter of the Good Friday agreement, which effectively recognises that partition, remarked at the weekend: "You can't decommission what's in people's minds." It seems clear that the republican movement has split irretrievably into the majority faction, who had decided by Easter that minds must be changed, and several small splinters that are too completely enmeshed in the politics of hatred to countenance such a change.
The political voice of these people comes through the 32 County Sovereignty Committee. It is no accident that this is led by Bernadette Sands-McKevitt, basing her stance upon the reputation and name of a dead hunger-striker, and that money is being raised for them by reactionary Irish Americans: the tyranny of the dead, and the ignorance of those living across the Atlantic comfortably afar from the "struggle". They may be few in number and perverted in psychology, but it is an ancient and potent combination: what can Gerry Adams and his new-look comrades do to neutralise it?
In ideological terms, not much. For all Adams's statements otherwise, the fact remains that the Good Friday agreement recognised reality by postulating arrangements for the existing six-county entity of Northern Ireland, albeit by building the Nationalist minority more closely into its governing structure than ever before, and institutionalising a level of links with the Republic previously held unacceptable by the Unionist majority. This level of imaginative but realistic politics cannot be grasped by the closed sectarian minds of "Oglaigh na hEireann", even when formally endorsed by about 95 per cent of nationalists on the whole island of Ireland. And the trouble with quartermasters is that they do not respond to democratic mandates.
What they do respond to, presumably, is force; so the question now is where the force is to be exerted from. Here it may help to look back to history. After the Anglo-Irish Treaty of 1921, the dissident republicans who refused to accept its terms took arms against the new Irish Free State in a civil war of episodic but horrifying brutality. The new government pursued its ex-comrades with unremitting ferocity, not only by internment but by executions: when people blenched at the 77 ordered by one minister, he riposted: "777 if necessary". The Civil War ended, the dissidents' arms were dumped, they eventually formed their own political party under Eamon de Valera which grudgingly entered the democratic process, and came to power a decade after giving up the armed struggle. They were faced in turn with a split from their own purist wing, who were - once again - pursued, interned (and allowed to die on hunger strike if thought necessary) by de Valera's government. The numbers prepared thus to suffer decreased; if an irreducible though tiny core remained, their stance was usually intellectual rather than activist. When the residual IRA mounted a short- lived bombing campaign in the mid-Fifties, there was an overwhelming consensus among Irish nationalists against its perpetrators. Those who support the Good Friday agreement in Ireland must hope that this repetitive drama will be played out once more.
Since three o'clock in Omagh last Saturday afternoon, that drama looks like the story of the House of Atreus, caught in a loop of inexorable and psychotic violence visited upon the innocent. If the process is to be short-circuited, the dissidents have to be choked off: Mr Aherne has already ambivalently hinted at internment; Mr Trimble has blamed the last atrocity on a lily-livered approach to decommissioning arms.
What seems clear is that the sheer random sadism of what happened in Omagh has pushed the dissidents further out to the edges of the increasingly dysfunctional "Republican family". Formerly condemned at last by the ex- hard men of Sinn Fein, they are even more marginalised than the IRA remnants of the late Fifties. By the same process, messrs Adams and McGuinness have lost any ground they had for equivocation. Their co-operation with their allies in the peace process must now be total: all the knowledge they have of their ex-comrades behind the atrocity has to be shared with the security forces in the interests of their own self-preservation as well as that of a democratic future, north and south.
For, if Irish history shows anything, it is that the answer will lie - as before - with those who were once closest to the murderers in "Oglaigh na hEireann", and who therefore now seem - to those deluded minds - the worst traitors of all. No wonder Mr Adams is keeping quiet for the moment; no wonder he and Mr McGuinness have been frantically guarding their backs by making gratuitous (and illogical) remarks about the death throes of Unionism over the past couple of weeks. The real struggle with their flat- earthers is beginning. Whatever Mr Adams's own past in the Seventies, anyone who believes in the Easter agreement must hope to see him occupying an authoritative enough position to protect it. If this may even mean the piquant spectacle of Mr Adams introducing internment as a minister in a northern ireland government, stranger things have happened in Irish politics - and in Irish history. And the previously unthinkable may well have to be embraced in order to proceed against the murderous wreckers who have now shown that they will unloose a river of innocent blood to destroy what was achieved last Good Friday.
Roy Foster is Carroll Professor of Irish History at Oxford University