Republican presidential frontrunner Donald Trump has unleashed a stunning verbal assault on his nearest competitor Ben Carson, saying US voters were "stupid" to believe the doctor's moving personal narrative and comparing him to a pedophile.
It was Trump's most aggressive campaign speech yet in his bombastic run for the 2016 Republican nomination, hurling sharp insults against several rivals including "weak-like-a-baby" Senator Marco Rubio and business executive "Carly whatever-the-hell-her-name-is" Fiorina.
The billionaire real estate tycoon pulled no punches during a Thursday night stump speech that devolved into a 95-minute rant in Fort Dodge, Iowa, the state that votes first in the presidential nomination process.
He reserved his harshest criticism for Carson, already under scrutiny for the details of what he has said was a violent adolescence in which he claims to have tried to stab another young man.
Trump flipped his belt buckle up and down, ridiculing Carson's claim in his 1990 autobiography "Gifted Hands" that the boy's belt buckle prevented the knife from entering his body.
"Anybody have a knife? Want to try it on me? Believe me, it ain't gonna work," Trump said, indicating that a buckle would provide no protection.
But in Carson's account, Trump said, "he plunged it into the belt and, amazing, the belt stayed totally flat and the knife broke."
"Give me a break," he fumed. "How stupid are the people of Iowa? How stupid are the people of the country to believe this crap?"
The caustic attacks were a world apart from Trump's restrained demeanor during Tuesday's Republican primary debate, where he issued no attacks on Carson.
It was a different story Thursday as Trump turned brusque.
During an interview with CNN, he repeated his accusation that Carson had a "pathological" temper, quoting directly from Carson's book, adding that it equates to the sickness of a child molester.
Hours later, Trump doubled down on the comparison at the rally in Iowa, where Trump and Carson are running neck-and-neck.
"That's like, I could say, you don't cure, as an example, a child molester," he told the crowd.
"If you're a child molester, a sick puppy, you're a child molester. There's no cure for that."
Trump also directed his ire at extremists in the Middle East, and President Barack Obama's policies there.
"I know more about ISIS than the generals do," Trump boasted, as he crudely summarized his plan to deal with the Islamic State extremist group and take the oil it uses to finance its operations.
"I would bomb the shit out of them," he said to loud applause.
"That's right: I'd blow up the pipes, I'd blow up the refineries. I'd blow up every single inch, there would be nothing left."