The pioneering Massachusetts program to provide health insurance for all citizens looks more and more successful with each passing month.

The number of uninsured has dropped  Massachusetts now has the lowest rate in the nation  and so have the number of those who turn to costly emergency rooms for routine care. And while the state has had to seek additional sources of revenue  mainly because of the program’s popularity  the gains in the first 21 months suggest that the plan could become a model for universal health coverage for other states or the nation.

Massachusetts enacted its ambitious health insurance reform two years ago under bipartisan leadership from then-Gov. Mitt Romney and a Democratic Legislature. Although Mr. Romney distanced himself from the plan during the Republican primaries, he was back to extolling its virtues in an opinion piece for The Wall Street Journal last month.

The plan requires everyone to take out health insurance or suffer a tax penalty and requires employers to offer coverage or pay a small assessment if they don’t. Low-income residents can enroll in an expanded state-federal Medicaid program or receive subsidies to pay all or part of the premiums for private insurance. Those who earn more than 300 percent of the federal poverty level (about $63,000 for a family of four) receive no subsidy but can buy private policies through a new insurance exchange at much lower rates than before.