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The outcome of the June 17 Greek legislative elections will not only determine whether Greece exits the eurozone, but it could also seal the fate of the entire postwar European project. According to the latest polls, the center-right New Democracy (ND) party and the Coalition of the Radical Left, known as Syriza, are in a dead heat. Taking first place is crucial, because it comes with a 50-seat bonus in parliament, which means that no government can be formed without the winner.

For its part, ND's chances hang on whether it can rally the voters who deserted the party in the last national elections on May 6. Those elections were an attempt, at least, at a power grab by ND's leader, Antonis Samaras. He had built his political profile by standing in opposition to the...