In the past month, four emergency room nurses ... have quit at the Eureka hospital where Matt Miele works. Around California — and the nation — nurses are trading in high-pressure jobs for a career change, early retirement or less demanding assignments, leading to staffing shortages in many hospitals. But burnout isn’t the only thing compounding California’s nursing shortage: The state’s new vaccine mandate for health care workers is already causing headaches for understaffed hospitals before it is even implemented. Some traveling nurses — who are in high demand nationwide — are turning down California assignments because they don’t want...