As the foundation notes, more people seemingly made up their minds about the law last month. The rate of those without an opinion on the Affordable Care Act dropped from 16 percent in June to 11 percent in July.
Historically, public opinion on the ACA hasn't changed much since it was enacted, despite some notable monthly swings. Kaiser pollsters said it's not clear what drove the change in opinion this month.
"Normally, when negatives go up, you can tie it to an event," said foundation chief executive Drew Altman in an interview. Events like a broken enrollment Web site, or people losing their health plans.
That doesn't seem to be case here, though. The poll was conducted before a federal appeals courts split on the legality subsidies in the 36 states with federal exchanges, and before House Republicans formally advanced plans to sue President Obama over his failure to enforce the law's employer coverage mandate. Yet, the poll was conducted after a string of surveys showing that the nation's uninsured rate has dropped significantly since Obamacare's coverage expansion took effect this year.
Kaiser's pollsters point out that most people still hear negative things about the law. People who said they discussed the law were about five times more likely to report that they heard mostly bad things about it, while people who said they encountered political ads about the law (53 percent) said those ads were mostly against it (19 percent versus 7 percent).
But that's pretty much always been the case, so it doesn't seem to explain the sudden spike in unfavorability. Altman said he couldn't really explain this month's finding.
"I think we're going to have to wait and see what this looks like in future months," Altman said. "It may be a blip."
Still, about six in 10 people said they’d prefer to keep the law and improve it. That includes a strong majority of Democrats (86 percent), most independents (58 percent) and almost a third of Republicans.