In the political roller-coaster since the first Provisional IRA ceasefire in 1994, Sinn Fein has at times been indulged to an extraordinary extent.
The blackest period in what republicans like to call the “peace process” came a decade ago, when the IRA robbed the Northern Bank and murdered Robert McCartney.
In the years prior to that, it spied at Stormont and broke into Castlereagh police complex.
Name another stable liberal democracy on earth in which a party inextricably linked with a paramilitary organisation guilty of such crimes would get within sight of power.
Yet in Northern Ireland, Sinn Fein must at all times be permanently at the heart of government, regardless of its conduct.
Even a standalone Conservative government seems reluctant to contemplate any other scenario. It would not be inclined to withstand the fury from Dublin, which – hypocritically – does not want Sinn Fein anywhere near power in the Republic.
Peter Robinson, DUP leader and first minister, said yesterday his party entered government with republicans on the basis of exclusive commitment to “democratic means through support for the police, the courts and the rule of law as well as the dismantling of the structures of their terrorist organisation”.
Of the crimes listed above, the most brazen was the robbery. Only a huge and sophisticated organisation could pull it off.
The good news is that there has been nothing like it since.
It is possible that the murders of Gerard ‘Jock’ Davison and Kevin McGuigan, like the murder of Paul Quinn, were the work of rogue Provisionals. In an organisation with such a past, violent volunteers are hardly in short supply.
It is depressing that Northern Ireland must be governed by a party that covered for such a group, but that is where we are.
However, if the McGuigan killing points to an intact IRA structure, then Sinn Fein must face specific sanction for once. If that means Stormont falls, David Cameron must ensure no green tinge to direct rule. As prime minister with a Tory majority, there is no excuse for any other response.