The campaign in Massachusetts is a reminder that Republican Scott P. Brown swept into the Senate three years ago, also in a special election, with an opportunity to break Democrats’ hopes of passing the health care law with a filibusterproof majority.

Mr. Obama and his political allies made enough moves to pass the law, anyway.

Yet while its passage still rankles most Republicans, voters in the Bay State have lived with the law’s equivalent, “Romneycare,” for seven years, said Mary Anne Marsh, a Democratic strategist in Boston.

“I think the role [health care reform] played in Brown’s win was always exaggerated in comparison to other factors in that race,” she added.

Fred Bayles, director of Boston University’s Statehouse Program, noted the state legislature passed its health care reform law with little fanfare under then-Gov. Mitt Romney in 2006.

“This was supported by Republicans and Democrats in the legislature,” he said. “There were no demonstrations.”