Mike Segar/Reuters Republican presidential nominee Donald Trump publicly renounced his long-held belief that President Barack Obama was not born in the United States. But many of his followers have not done the same, polls show.

Donald Trump, one of the loudest proponents of the conspiracy theory that President Barack Obama wasn’t born in the U.S., publicly abandoned the idea last week. “President Obama was born in the United States, period,” he said.

If anyone could help convince members of the GOP to stop questioning the president’s birthplace, you might expect it to be their presidential nominee ― especially since he’s spent years leading the crusade. But Trump may only be able to stuff the genie partly back into the bottle.

In the wake of Trump’s statement, Republicans are now less likely than they were in January to say Obama was not born in America, but a substantial majority still refuse to say affirmatively that he was, a new HuffPost/YouGov poll finds.

“People will go to great lengths to cling to their prior beliefs, even in the face of a good deal of contradictory evidence. Trump’s statement is just one more piece of contradictory evidence. It doesn’t seem to have been enough to move people from one side to the other,” said Joanne Miller, a political scientist at the University of Minnesota who’s researched the impact of ideology on conspiracy theories.

“For Republicans who have clung to the belief that Obama was not born in the U.S. for a very long time, it is difficult to now admit they were wrong, even when their presidential nominee tells them they are,” she said.

It’s discouraging that Trump’s retraction does so little to reduce belief in the birther myth. Brendan Nyhan, Dartmouth College

In January, 21 percent of Republicans surveyed by HuffPost/YouGov said Obama was born in the U.S., 53 percent said he was not and 26 percent said they weren’t sure.

In this week’s poll, by contrast, 33 percent of Republicans say Obama was born in the U.S., 39 percent say he was not and 28 percent say they aren’t sure.

Meanwhile, 47 percent of Republicans now say there are still reasons to doubt that Obama was born in the United States, while 18 percent say there were reasons to doubt that Obama was born here, but those questions have now been settled. Just about one-fifth say there has never been any reason to doubt that Obama was born in America.

“It’s discouraging that Trump’s retraction does so little to reduce belief in the birther myth,” said Brendan Nyhan, a political scientist at Dartmouth College who’s studied the difficulties of correcting political misinformation. “But we shouldn’t be surprised ― even the release of Obama’s long-form birth certificate had a relatively small and short-lived effect.”

In order to test the effects of Trump’s statement on public opinion about Obama’s birthplace, the HuffPost/YouGov poll divided survey respondents into two groups and asked each group slightly different questions. Half were simply asked, “Do you think Barack Obama was born in the United States, or not?” The other half were first told about Trump’s statement that Obama was American-born.

About the same percentage of Republicans in both groups said they believed Obama was born in America ― 32 percent of those who didn’t see Trump’s quote, and 34 percent who did, staked out that position.

But while 46 percent of those who weren’t prompted with Trump’s quote said that Obama was not born in America, 33 percent of those who were told about his quote still felt that way. Respondents presented with Trump’s statement were more likely to hedge by saying that they weren’t sure whether Obama was born in the U.S. or not.

Democrats and independents were also divided into two groups, but showed considerably less variation in their answers.

The Huffington Post Being told that Donald Trump had renounced his birther stance led fewer Republicans to say they were sure Obama was born outside the U.S.

The experiment lays bare two of the competing rationales that can motivate survey-takers.

On the one hand, people tend to jump at the chance to endorse any negative statement about their candidate’s political opponents, a tendency that’s only been exacerbated by increasing political polarization in recent years. That’s always been part of the appeal of birtherism for many Republicans, who loathe Obama and are prone to agree with any statement that casts him in a bad light.

On the other hand, people also tend to rely on partisan cues when answering surveys, making them more likely to take a particular stance on an issue if they think it puts them in line with their party’s leaders. HuffPost/YouGov polling last year found that, for instance, Republicans were far more likely to support universal health care when the idea was attributed to Trump, while Democrats were more enthusiastic about the concept when it was attributed to Obama.

That leaves Republicans who’ve supported birtherism caught between either abandoning their belief or opposing their presidential nominee.

“The best they can do, while still ‘saving face’ is to move to the ‘uncertain’ category,” Miller said. “A full reversal would be too identity threatening.”

From here, she predicted, one of two things could happen. Republicans could continue to soften in their beliefs, eventually admitting that Obama was, in fact, born in the U.S.

Or ― in perhaps a more likely scenario ― a “boomerang effect” might kick in as those who originally believed the birther theory are threatened but unwilling to change their minds, and instead succeed in re-convincing themselves of what they believed in the first place.

Some survey respondents are already dealing with the cognitive dissonance by deciding that Trump didn’t really mean what he said. More than 40 percent of Republicans who don’t believe Obama was born in the U.S., for instance, say they think Trump himself secretly still believes the same thing.

Overall, 61 percent of Americans say that Obama was born in the U.S., up from 50 percent in January. Independents were also more likely to acknowledge that Obama was born here ― in the most recent poll, 59 percent said so, up from 43 percent in January. (Perhaps not coincidentally, Obama’s approval rating has also improved significantly over the past nine months.)

Twenty-nine percent of Americans don’t think Trump ever believed Obama was born outside the U.S., while 19 percent think he’s changed his mind on the issue and 27 percent believe that the Republican nominee is still a birther at heart.

A 51 percent majority of Americans, including 80 percent of Democrats and 47 percent of independents ― but only 18 percent of Republicans ― say that Trump should apologize to Obama for having questioned his birthplace.

The HuffPost/YouGov poll consisted of 1,000 completed interviews conducted Sept. 17-Sept. 19 among U.S. adults, using a sample selected from YouGov’s opt-in online panel to match the demographics and other characteristics of the adult U.S. population.

The Huffington Post has teamed up with YouGov to conduct daily opinion polls.You can learn more about this project and take part in YouGov’s nationally representative opinion polling. Data from all HuffPost/YouGov polls can be found here. More details on the polls’ methodology are available here.

Most surveys report a margin of error that represents some, but not all, potential survey errors. YouGov’s reports include a model-based margin of error, which rests on a specific set of statistical assumptions about the selected sample, rather than the standard methodology for random probability sampling. If these assumptions are wrong, the model-based margin of error may also be inaccurate. Click here for a more detailed explanation of the model-based margin of error.

Editor’s note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims — 1.6 billion members of an entire religion — from entering the U.S.

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