For the past few years, pollsters have asked about a thousand or so Americans the same question: Does the government have an obligation to ensure all Americans have health care?

They've found a remarkable shift, with Americans swinging sharply toward the belief that the government ought to play a very large role in the health care system.

Specifically, the percentage of Americans who think the government has an obligation to ensure coverage to all citizens has risen from 42 percent in 2013 to 60 percent in 2017.

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An 18-point swing in just four years is a remarkably fast change in the world of public policy polling.

"When we reviewed everything, nothing else in our data was close to 18 points," says Harvard's Robert Blendon, who published the data in today's New England Medical Journal. See chart here.

To put that in context: Although much fanfare has been made out of improving views of the health care law, when Blendon averaged together national polling, he found the law's favorability ratings had only risen 5 percentage points.

Blendon attributes the change in attitudes to Americans thinking through the consequences of repealing the Affordable Care Act, resulting in millions losing coverage. The question didn't ask about Obamacare specifically, a highly polarizing law. Instead, it asked generally about the government's role in providing coverage.

"People have not fallen in love with the ACA," Blendon says. "What they fell in love with was the idea that the federal government can't drop 30 million people from coverage all at once, that there was a responsibility for universal coverage."

His article also finds that government health programs, like Medicaid, generally poll better than the expansion of private coverage through insurance subsidies.

Most Republican voters say they do not want to cut the number of people covered through Medicaid, the public program that provides health insurance to low-income Americans. But most Republicans wereopen to cutting subsidies for private insurance.

"Medicaid emerged out of this debate with an awful lot of sympathy," Blendon says. "The majority of every group we looked at did not want to see the number of people covered by the program cut."

For me, Blendon's findings (and the chart above, in particular) do a lot to explain why Republicans have so far failed to deliver on their promises to repeal and replace the Affordable Care Act.

It's not just the fact that millions of Americans now rely on the law and its programs for coverage. And it's not the rise in Obamacare's popularity, which has been relatively meager.

It's also a fundamental shift in attitudes that has happened after the Affordable Care Act passed, where Americans became more accepting of a larger role for the government in health care. For all the attacks on the health law as a "government takeover" of health care, this polling suggests voters are kind of okay with that.