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Sammy Wilson of the DUP said it first, the good thing about the policing and justice deal that's been struck was that it had been made in Ulster. On Friday morning, Martin McGuinness of Sinn Féin quoted Wilson approvingly: that's how he felt too, McGuinness said, although he added that his Ulster was a nine-county one while Wilson's was confined to six. Neither man has much appetite for being told what to do by British ministers, but for republicans it goes deeper. Transfer of policing and justice is an integral part of a political strategy they've been pursuing since the Good Friday agreement and earlier.

A few days ago, Gerry Adams spoke of policing and justice repatriation as "another staging post". The phrase jangled some unionist nerves but it chimed harmoniously with many...