MADRID — Spain’s flurry of regional elections over recent months — most crucially in Andalusia this Sunday — has delivered an ominous message to the ruling Socialist Party of Prime Minister Pedro Sánchez ahead of next year’s general election. As Spain’s most populous region, Andalusia was of particular importance, and the Socialists’ heavy defeat was a historic and humiliating blow for a party that once regarded it as one of its strongholds. The conservative People’s Party, led by Andalusian