When Mayor Bill de Blasio created a universal prekindergarten program and a near-universal 3-K program in New York a decade ago, it was rightly described as a miracle. But in many ways, that undertaking was far simpler than what Mamdani is promising. He aims to provide high-quality, year-round care to toddlers and infants as young as six weeks old, while setting day-care workers’ earnings “at parity” with those of public-school teachers. It’s a cosmically aspirational set of goals, and it faces a steep set of obstacles. But if he can pull it off, the scheme would transform New York’s demography and economy, constituting one of the most radical examples of policy entrepreneurship in recent memory.