In late spring 2005, Mitt Romney gathered with a dozen top policy and political advisers in a conference room near the governor’s suite on the third floor of the State House. For two years, they had grappled with the abstruse complexities of health care reform, sifting data, evaluating input from experts, and testing theories to craft a plan that would expand coverage to nearly everyone in the state and not break the bank. This was a bold move for a first-term Republican governor, some of whose more conservative advisers doubted the wisdom of a foray deep into policy turf long...