He’s called Ben Carson a child molester and insulted Iowans by calling them stupid. Even GOP political strategists think it raises the possibility that Trump’s seemingly sturdy floor of support could begin to give way.

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First he compared Ben Carson to a “child molester” in a nationally televised interview. Then, at a campaign rally, Donald Trump asked for someone to come try to stab him in the abdomen, twisting his own belt buckle as if to prove that Carson’s account of having knifed a friend, as a wild-tempered youth, had to have been a lie.

In the same speech — a 95-minute rant in Fort Dodge, Iowa, on Thursday night that left his listeners stunned into silence — Trump managed to insult a good portion of the electorate in Iowa, where Republicans will cast their ballots in 79 days, by saying voters there would be “stupid” to believe in Carson.

By Friday afternoon, when he posted a video mocking Carson as either a would-be killer or a pathological liar, the more pressing question seemed to concern Trump’s candidacy and whether he will ever be able to convert it from a personality-driven crowd attraction into a persuasive case for the presidency that can attract a majority of Republican primary voters.

The front-runner all summer, Trump has struggled to crack through a ceiling in the Iowa polls of about 30 percent, in large part because of fierce recent competition from Carson, the mild-mannered retired neurosurgeon who has won a following with evangelical voters with his story of spiritual redemption.

But now, with his scathing attacks on Carson and his supporters that some Republicans believe will backfire, it raises the possibility that Trump’s seemingly sturdy floor of support in those polls could begin to give way.

“How stupid are the people of Iowa? How stupid are the people of the country?” Trump said Thursday night, of voters who believe Carson’s story. “Don’t be fooled,” he said of Carson’s story of his decades-old religious awakening.

Dave Carney, a Republican political strategist who ran Rick Perry’s presidential race in 2012, speculated that the remarks could be deeply damaging.

“He’s walking on a tightrope,” Carney said of Trump. “He loves the applause of the crowd 100 stories down. But when you start to make fun of being born again and redemption and Christian faith in our party, you can talk yourself right off the tightrope.”

Carson, who came under scrutiny last week over whether he had embellished details of his background, including his story of having assaulted someone with a knife, declined to be baited into a fight Friday, sidestepping what he called Trump’s “gratuitous attack” but saying he would not participate in the “politics of personal destruction.”

Trump has survived — even thrived — after the sort of verbal recklessness that would have doomed other candidates: his characterization of Mexican illegal immigrants as rapists and drug dealers, his denigration of Sen. John McCain’s years as a prisoner of war in Vietnam, and his derogatory comments about a Fiorina, as well as Megyn Kelly of Fox News and other women.

But some Republicans said Trump’s 24-hour spree of over-the-top effrontery could at last signal his eventual derailment, given that it exacerbated long-held questions about his temperament and unstatesmanlike style.

“Trump’s attacks on Carson could be the hole in the dike,” said Edward Rollins, a veteran Republican consultant, referring to Trump’s core of supporters. “Many Republicans didn’t like McCain. It was also early in the campaign and many were viewing Trump as a protest candidate. Now he is viewed as a front-runner and potential nominee. To attack Carson yesterday as viciously as he did may make voters take a second look.”

Several pollsters said Trump’s latest remarks had created the most potentially damaging moment of his campaign. But they were unsure how many die-hard Trump supporters would stick with him no matter what he says.

“Trump has had what looks like a hard floor of support in Iowa — at least 20 percent — but a hard floor one day may not be a hard floor a week later if the candidate has not created a bond with voters” through advertising as well as speeches and debate performances, said Peter Brown, assistant director of the Quinnipiac University Poll. “This is perhaps the strongest language that Trump has used to date, and we’ll soon see if voters accept it.”

Ed Goeas a longtime Republican pollster, said the biggest problem for Trump may be the use of the word “stupid.” Voters may forgive many things, like insulting Mexicans and McCain, he said, but they do not like being called dumb.

“That’s not the way to endear himself to Iowans, the very voters who he is trying to pull away from Carson with these attacks,” said Goeas, who previously advised a former Republican presidential candidate, Gov. Scott Walker of Wisconsin. “For the first time in this campaign, I feel like this might be the moment that Trump needs to apologize for something.”

Matt Moore, chairman of the South Carolina Republican Party, which holds the first primary in the South in mid-February, said Trump risked turning off evangelical and conservative voters by attacking Carson, a man who enjoys wide respect from them.

“It will be impossible to win the Republican nomination, much less the White House, by slashing and burning down the field,” Moore said. “Politics is addition and multiplication, not division and subtraction. It’s simple math.”

For that math to work in Trump’s favor, he needs to start spending money to build a serious political operation in multiple states, Republicans said, as well as on political advertising so voters can see different facets of him.

Candidates do not win by simply trusting that voters will read about their speeches on social media or in newspapers, or catch snippets of their remarks on television, Republicans said. Such connections are impersonal and less effective than broadcasting positive commercials and meeting voters at scores of small-scale events where they can get a feel for candidates.

That is the decision Trump faces: how to grow a candidacy that has been nurtured on bombast, but deprived of spending. His aides continue to promise that he will soon buy television ads, but none have materialized.

Still, John McLaughlin, a Republican pollster who briefly advised Trump in 2012 when he considered a presidential run, said Trump remained “the best vessel for voters who are deeply frustrated with politics.”

“He can say these things and get away with it because the race really isn’t about him, but about voter anger at Washington and President Obama and also at Republicans who can’t get things done,” McLaughlin said.

“Trump is acting from his gut with these attacks,” McLaughlin added, and his instincts have served him well so far. “His gut is, he needs to take Carson on.”