In 1994, New Jersey decided to stop setting aside money in a fund to pay for health care for its retired public workers. The savings paved the way for a big tax cut. Meanwhile, hundreds of thousands of public workers were being told that as long as they worked 25 years, the system would provide virtually free health care for them when they retired, often when they were as young as 55. No one added up the cost — until now. It turns out that New Jersey will need about $58 billion, in today’s dollars, to provide all the care...