The future of the Catholic-Protestant power-sharing government in Northern Ireland is hanging by a slender thread with First Minister Peter Robinson’s decision Thursday to step down, along with all but one of his ministers, because of a series of disputes. Democratic Unionist leader Robinson left one party figure, Arlene Foster, in place as temporary first minister and finance minister, but the coalition government has been seriously weakened by developments and may ultimately be suspended, leading to a restoration of direct British rule from Westminster. The crisis stems in large part from a police finding that that Irish Republic Army dissidents...