The chart above reflects the results of NBC News / Wall Street Journal polls for the last six years. The latest poll was done between April 28th and May 1st of a national sample of 900 adults, with a margin of error of 3.27 points (and all of the polls would have about the same size sample and margin of error).
The polling was on Obamacare. Note that before January of 2017, the public thought Obamacare was a bad idea. It was easy for many to believe that because the Republicans kept telling them it was -- and that they had a plan that would be better.
But then Trump was elected, and the Republicans had majorities in both houses of Congress. They had the opportunity to do away with Obamacare and replace it with their "better" plan. But they were exposed as liars. They not only didn't have a better plan, but they didn't have any plan at all -- and they still don't.
Now that the public knows the GOP has no plan, the numbers have flipped. More people think Obamacare was a good idea now than think it was a bad idea.
This doesn't mean they think Obamacare solved the problems in our health care system. They don't. They know serious problems still exist, and they want them fixed. They just know now that the GOP can't fix them.