There have been so many acts of brutality in Northern Ireland over the past 36 years that it is surprising that one murder has proved so significant. The killing of Robert McCartney has plunged the IRA into crisis and its statement on Tuesday has made matters far worse. The arrogance of its revelation that it had offered to shoot those responsible for Mr McCartney’s death is just as chilling as the proposed “remedy”. It has revealed publicly the assumption that the self-appointed armed “representatives” of the republican community have the right to exercise a power of life or death in parts of the Province. The IRA’s words were beyond belief. Will it now “shoot” the author of the press release that has caused so much controversy?

They were also unusual for an organisation which has often combined an enthusiasm for crime with a flair for public relations. Both Sinn Fein and the IRA badly underestimated the impact of the killing of Mr McCartney and the heroic resolve of his partner and sisters. Gerry Adams had clawed back some of the ground lost by his invitation to the McCartney family to attend the recent Sinn Fein conference and hear him call on those with information about Mr McCartney’s fate to come forward. What advance he may have achieved through this publicity stunt has been marginalised by the IRA’s bizarre and callous statement.

All of this leaves Mr Adams, Sinn Fein and the IRA further compromised. The McCartney family and campaign will not go away and they will settle for nothing less than the prosecution of suspects in open court. The IRA either has to deliver prominent supporters into the hands of the Police Service of Northern Ireland (PSNI) or refuse to do so and face the condemnation of what it regards as its core constituency. It is not, alas, that surprising that the IRA pledged to kill those implicated in the McCartney outrage. Having them “disappear”, by one means or another, would have been regarded by the IRA as the least bad outcome in the awkward circumstances.

If past form is any indication, a rattled IRA and Sinn Fein will try to play for time. They will hope, improbable as it seems, that the collective impact of the Northern Bank robbery and the McCartney saga will gradually fade. A willingness to operate on the basis of “the long game” is embedded in them.

It will not do in these conditions. Mr Adams, in particular, needs to switch to the short game if he and his party are to have any credibility as actors in the democratic realm and partners in any revived peace process. He must make some dramatic initiatives to restore confidence among nationalists as well as Unionists. They include being willing to swallow the humiliation of the IRA figures linked to Mr McCartney’s murder being placed on trial, acknowledging the PSNI as the sole legitimate policing body in Ulster and ensuring that the IRA orders its “volunteers” to cease all criminality, a pro-cess to be assessed by the International Monitoring Commission. Mr Adams might retort that he has strived mightily for the peace process and deserves credit. But others have also made huge sacrifices and sense that they have been betrayed by republican leaders. Mr Adams’s apologists claim that the IRA would split if there were an effort to wind it down. Yet there is already a far more important split evident: between the IRA and the ideals and values of everyone else in Ulster.