Ben Carson, who has reached the top of polls in the GOP primary in part through telling his compelling personal story of surviving a difficult childhood to become a world-renowned neurosurgeon, is now facing intense scrutiny about whether he has exaggerated or made up details of his early life.

A Friday report published by Politico cast doubt on claims made by Carson in his best-selling autobiography “Gifted Hands” that he was “offered a full scholarship” to attend West Point. Carson’s campaign, and the candidate himself, responded that the offer was made at an informal meeting with West Point representatives but that he never followed through on such an opportunity because he wanted to pursue a career as a doctor, a claim consistent with his writing.

On Thursday, CNN published a story in which the network said it could not find anyone who grew up near Carson in Detroit to corroborate several anecdotes the doctor has told about his childhood.

Some of his neighbors and friends from that period, speaking to CNN, could not recall incidents Carson has spoken or written about that include him allegedly being stopped by his brother from punching his mother, attempting to stab one of his friends during an argument and hitting a kid in Carson’s neighborhood with a rock, breaking his glasses and smashing his nose.

Carson has strongly denied he falsified these details of his childhood, accusing CNN of a "smear campaign" in an interview on Fox News on Thursday. On Friday, he accused the media of conducting a "witch hunt."

For Carson, this type of scrutiny is perhaps the biggest threat yet to his surging campaign, because the retired neurosurgeon is relying heavily on his personal story to connect with voters.

Carson has few detailed policy plans, and those he has released, such as his proposal to impose a system akin to tithing to replace the current federal tax code, have been derided by critics.

And the candidate at times struggles to discuss even basic details of government and history, most notably when he erroneously declared this week that none of the signers of the Declaration of Independence had previous political experience.

Earlier this week, a video surfaced from the 1990’s in which Carson discussed his belief that the pyramids in Egypt were built by the biblical figure Joseph to store grain rather than as burial chambers for the pharaohs. When asked about those statements this week, Carson “it is still my belief,” adding, “The pyramids were made in a way that they had hermetically sealed compartments. You wouldn’t need hermetically sealed compartments for a sepulcher. You would need that if you were trying to preserve grain for a long period of time.”

Instead of a traditional campaign, Carson, a Seventh-day Adventist, speaks in the language of evangelical Christians, talking about how prayer and faith helped him get out of poverty. Carson often tells a story about how, while an undergraduate at Yale, he was worried about passing a chemistry test. But the night before the test, he had a dream that showed him which questions would be asked and their answers. Carson attributes that dream to God.

Carson’s stories about being an angry child are part of this narrative.

“God can do anything, because He changed me," he writes in Gifted Hands.

In polls, Carson leads Trump in Iowa largely because of the doctor’s strong support among evangelical Christians.

While most of his 2016 rivals have been silent on these controversies, Donald Trump blasted Carson in a Twitter message on Friday.

“WOW, one of many lies by Ben Carson! Big story,” the real estate mogul wrote, with a link to the Politico piece.

On Friday, conservative activists largely defended Carson, arguing Politico had over-hyped its piece about him. But the danger for the doctor is what befell New Jersey Gov. Chris Christie. There has never been any proof that Christie knew of his aides’ plans in 2013 to close a bridge in New Jersey as an act of retribution against a local mayor they did not like. Publicly, influential Republicans strongly defended Christie and suggested the media was obsessed with attacking the governor.

Privately, Republicans suggested the scandal, true or not, damaged Christie’s political viability. And in his presidential campaign, Christie has struggled, with mayor GOP donors and activists embracing other candidates like ex-Florida Gov. Jeb Bush and Florida Sen. Marco Rubio.

In a 15-candidate field, GOP voters have plenty of choices. They could simultaneously say the media is unfairly beating up on Carson while still also abandoning him for candidates with similar views, like Trump or Texas Sen. Ted Cruz.

Of course, Trump has survived a number of controversies during this campaign while remaining at the top of polls. Carson was roundly criticized in September for suggesting he did not think a Muslim should be elected president, and he went up in the polls amid the controversy.

“Prediction: Dr Carson's numbers will go up + his fundraising will spike as a result of media reports of fabrications. Cuz, it's 2016 y'all,” said Ana Navarro, a Republican strategist and a backer of Jeb Bush, in a Twitter message on Friday.