Complex sentence: His largest donors came from the insurance, health professionals, and real estate sectors, with the California Association of Realtors, the California Chamber of Commerce, the California Medical Association, the California Building Industry Association, and the California Dental Association his largest contributors.
Split into simpler sentences: His largest donors came from the insurance, health professionals, and real estate sectors. The California Association of Realtors, the California Chamber of Commerce, the California Medical Association, the California Building Industry Association, and the California Dental Association were his largest contributors.