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WASHINGTON — As the Affordable Care Act, or Obamacare, turns 10 years old on Monday, the health care law is as popular as it has ever been, according to new numbers from the latest NBC News/Wall Street Journal national poll.

Forty-two percent of all registered voters believe the law is a good idea, compared to 35 percent who think it's a bad idea, while 23 percent don't have an opinion.

The difference between good idea and bad idea — plus-7 points — is as high as it has been since the NBC News/WSJ poll began tracking the legislation more than 10 years ago. (It was an equal plus-7 in April 2009, well before Congress passed the legislation.)

President Barack Obama signed the health care legislation into law on March 23, 2010.

Not surprisingly, attitudes about Obamacare are split along partisan lines in the poll.

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Eighty percent of Democratic primary voters, as well as 72 percent of all registered voters who describe themselves as Democrats, say the Affordable Care Act is a good idea.

That's compared to 72 percent of Republican voters in the poll who say it's a bad idea.

Among independents, it's 37 percent good idea, 23 percent bad idea and 39 percent no opinion.

Looking to the future beyond the Affordable Care Act, the NBC News/WSJ poll also finds that a public insurance option is more popular — especially among Republicans and independents — than a "Medicare for All" single-payer system is.

Seventy-three percent of all voters say they "strongly" or "somewhat" support allowing people under age 65 the option to buy their health care coverage through the Medicare program just like one might buy private insurance.

That includes 81 percent of Democratic primary voters, 81 percent of all Democrats, 76 percent of independents and 63 percent of Republicans.

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By contrast, just 43 percent of all registered voters say they support adopting a Medicare for All single-payer system in which private health insurance would be eliminated and all Americans would get their health care coverage from one government plan.

A combined 67 percent of Democratic primary voters and 68 percent of all Democrats in the poll say they back Medicare for All — similar to the exit poll findings in some of the early Democratic nominating contests.

But that's compared to 51 percent of independents and just 8 percent of Republicans who agree.

The NBC News/WSJ poll of 900 registered voters was conducted March 11-13, and it has an overall margin of error of plus-minus 3.3 percentage points.