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On Tuesday the Bulgarian government confirmed what most of the world has known for months: The bombing of a bus carrying Israeli tourists in the Black Sea resort of Burgas last July 18 was carried out by members of Lebanon’s Hezbollah organization. The results of an official investigation present leaders of the European Union with a reality that will be difficult to ignore. They must decide whether to allow a terrorist attack on E.U. territory to go unpunished or to sanction a movement that is both an Iranian proxy and the dominant party in the Lebanese government.