The Affordable Care Act brought the rate of uninsured Americans to a record low 9 percent in 2015. It's the major achievement of the controversial health care law and one the Obama administration likes to tout whenever it can.

Health and Human Services Secretary Sylvia Burwell did just that in an interview with NPR on Tuesday.

"We have the lowest uninsured rate in the nation's history," Burwell said. "Twenty million Americans have insurance that didn't have insurance before the Affordable Care Act. For many people, they consider it just a basic part of their health care."

But many of those surveyed in a new NPR/Ipsos poll got it wrong. About half believed that the number of people without insurance had increased or stayed the same, or said they didn't know what the law's effect has been on insurance coverage.

That was a failure of communication on the part of the Obama administration, says Bill Pierce, a senior director at APCO Worldwide, who advises health care companies on strategic communications.

"They needed to use the president more," said Pierce. "If this was his No. 1 achievement, and something he was proud of doing, it was the kind of thing that he needed to be out there and talking about all the time."

Democrats were better informed than Republicans, with 54 percent of Democrats saying the law had reduced the number of people without insurance, compared to 41 percent of Republicans.

One problem, Pierce said, is that the law was passed in 2010 but didn't go fully into effect for years. In that time, the website that housed the insurance exchange, the most public part of the program, failed.

"By the time the insurance rate started to fall, a lot of minds were already set," he said.

NPR's poll was designed to gauge the public's knowledge of some basic aspects of the U.S. health care system. The results come as Republicans on Capitol Hill are working to repeal the law. The Senate early Thursday morning passed a measure taking the first step toward dismantling the law.

While many people in the poll were misinformed about the big picture when it comes to Obamacare, they had stronger knowledge about the details of the law.

The majority of those surveyed know that the ACA protects people with pre-existing conditions from being refused coverage and that it requires insurance companies to pay for preventive care.

However, the heated debate during the 2008 presidential race over so-called "death panels" left a mark.

About a third of those surveyed believed Obamacare places limits on end-of-life medical care and another half were not sure. Only 18 percent correctly said that no such limits exist under the law.

Beyond Obamacare, many people had a good grasp of the overall quality of the U.S. health care system.

The majority was aware that Americans generally pay more for health care than people in other countries and that even so, health care outcomes in the U.S. do not have "the best results in the world."

The poll also reiterated findings from a separate survey from the Kaiser Family Foundation last week that showed that people are about evenly split on their view of the Affordable Care Act.

Still, most people don't want lawmakers to repeal the law until they have a replacement plan in place. Only 14 percent favor repeal without a replacement plan.

That message seems to have gotten through to lawmakers. Earlier this month, Republican leaders in the House and Senate were advocating an immediate Obamacare repeal, with a slow phaseout while they consider ways to replace the law so people who have insurance can still get it.

But many lawmakers walked those plans back this week in statements and via Twitter. Some, including President-elect Donald Trump, said they did not want to see a repeal until a replacement is ready.

"We're going to be submitting, as soon as our secretary is approved, almost simultaneously — shortly thereafter — a plan. It will be repeal and replace. It will be, essentially simultaneously," Trump said in a news conference Wednesday.

The poll surveyed 1,011 adults on Jan. 4 and 5, 2017.

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