Long Volkswagen's most reliable profit driver, luxury sports car maker Porsche has become its biggest problem, creating a road bump for CEO Oliver Blume's restructuring plans at Europe's biggest carmaker ▻ ↧ Porsche's decline from crown jewel to millstone for parent Volkswagen Less than four years after its record listing, Porsche ‌has turned into a poster child for the broader group's woes, dethroned in the once-lucrative Chinese market and bruised from costly missteps in the transition to electric.