Three years ago, Massachusetts passed the most sweeping healthcare bill in the country, adopting a plan that closely resembles the proposals being considered by Congress. It is a plan that now offers powerful lessons for the whole nation. The state's system, like the proposals moving toward votes in the House and Senate, focused on three goals: making medical insurance almost universal, fostering competition through a regulated insurance exchange, and helping low-income workers pay for coverage. Today, Massachusetts leads the nation with 96% of its residents covered by insurance -- an even larger share than some of the plans before Congress...