For some Republican presidential candidates, the party's first three primary debates have been pivotal proving grounds that have strengthened their campaigns or shaken their supporters.
Ben Carson isn't among them.
The famously mild-mannered Carson has largely avoided making headlines in the widely watched televised events, often willing to cede the spotlight to more verbose rivals and finding himself overshadowed in policy discussions. Yet the retired neurosurgeon's standing with voters in preference polls has only gotten better.
"The political language and the traditional prism through which we evaluate candidates essentially does not apply to Ben Carson," said Phil Musser, a Republican strategist.
It's unlikely Carson will again shrink into the background Tuesday when the eight leading GOP candidates meet in Milwaukee for their fourth debate. Now viewed as a front-runner for the Republican nomination, Carson faces intense scrutiny about the veracity of his celebrated biography, which has been central to his connection with voters.
His campaign manager, Barry Bennett, said Carson was prepared to be far more aggressive in the debate than he has been in the past and is "a lot more fired up" after facing several days of questions about his past.
"He will vociferously stand up for himself," Bennett said. "He's not going to attack anybody. But if somebody goes after him, they're going to see a lot more 'back at 'em' than they ever saw before."
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While pieces of Carson's background had been challenged earlier in the campaign, the questions ballooned last week after CNN reported it could not find friends or confidants to corroborate the story, told in his widely read autobiography, of unsuccessfully trying to stab a close friend when he was a teenager.
Later in the week, Politico examined Carson's claim of having received a scholarship offer to attend the U.S. Military Academy and The Wall Street Journal said it could not confirm anecdotes told by Carson about his high school and college years.
In a GOP primary where bashing the media is in vogue, Carson could come out ahead if the moderators of Tuesday's debate on Fox Business Network are seen as unfairly piling on. Carson's campaign was active in the effort to change how the party's debates are run after several candidates expressed unhappiness with moderators from CNBC at an event two weeks ago.
Yet some Republicans say Carson must walk a fine line between defending himself, and sticking with the calm and quiet demeanor that has so far been a draw for voters.
"Will viewers and voters see the unflappable surgeon they have been inclined to support or will a more combative Carson emerge?" said Matt Strawn, the former chairman of the Iowa Republican Party. "If the latter, his standing may well suffer if he appears to be yet another politician trying to out-outrage the others on stage."
Carson's response will likely be influenced by the way his rivals handle the matter. So far, most have sided with Carson, saying he's been unfairly treated by the media.
"They went too far with Ben Carson," Kentucky Sen. Rand Paul said Monday. "It's just kind of silly. They are trying to paint it to his integrity and I think that that's not fair."
The most likely candidate in the main event to challenge Carson is Donald Trump. The real estate mogul has been at the top of Republican primary polls for months, but began to level sharp criticism at Carson after he started challenging Trump's front-runner status.
Trump has seized on the inconsistencies of Carson's biography, repeating a long list of examples of potential exaggerations and unproven claims during recent television appearances. That includes repeating Carson's assertion that he had a "pathological" problem with his temper.
Speaking in front of thousands at a rally in Springfield, Illinois on Monday evening, Trump sharpened his criticism of Carson in a preview of potential lines of attack.
"With what's going on with this election, I've never seen anything like it. People are getting away with murder," said Trump, betraying his first signs of exasperation at Carson's success in the polls. "If you try and hit your mother over the head with a hammer, your poll numbers go up. I never saw anything like it!"
Also in the main debate Tuesday are Marco Rubio and Ted Cruz, a pair of senators enjoying a burst of momentum following their strong performances in the last contest; former Florida Gov. Jeb Bush, who is in the midst of an attempted campaign reset; and businesswoman Carly Fiorina and Ohio Gov. John Kasich.
Missing from the lineup are New Jersey Gov. Chris Christie and former Arkansas Gov. Mike Huckabee. Both were dropped from the top-tier debate with low poll numbers in national surveys, sparking criticism for the way networks hosting the debates have determined participation.
Christie and Huckabee will instead appear in an earlier undercard debate, along with Louisiana Gov. Bobby Jindal and former Pennsylvania Sen. Rick Santorum.
"We're not whiners and moaners and complainers in the Christie campaign," Christie said on Fox News Monday. "Give me a podium, give me a stage, put the camera on, we'll be just fine."
Associated Press writers Brian Bakst in Minnesota, Jill Colvin in New Jersey and Steve Peoples in Milwaukee contributed to this report.
