At the peak of his power, Russian President Vladimir Putin thought he could use his energy weapon to impose his will across Europe. Now Moldova — with a population of only 2.5 million — is emerging as the last truly vulnerable energy target in his flailing campaign to destabilize governments in the neighborhood taking a pro-EU trajectory. But no matter how hard Putin tries to turn the energy screws to topple the administration, Moldova’s government is doggedly resisting. Only last week Russian missile strikes triggered blackouts in half the country and last month Gazprom slashed gas supplies by a third,...