Determined to regain his front-runner status, Donald Trump is going after Ben Carson, the retired neurosurgeon, who has become the new star in the still-crowded field of Republican White House hopefuls.

"If I did the stuff he said he did, I wouldn't be here right now," the real estate tycoon said about his challenger, as he addressed a crowd in the crucial early-caucus state of Iowa, The Washington Post reported.

Trump did not mince words when it came to addressing the recent controversy over accounts in Carson's autobiography. The passages suggest the physician had a violent streak as a youth, but the stories have been questioned by media outlets and some of his rivals.

"It would have been over. It would have been over. It would have been totally over," he added. "And that's who's in second place. And I don't get it."

Trump went so far as to compare the 64-year-old Carson to a "child molester," suggesting his admission of childhood anger pointed to an incurable "pathological disease," the BBC noted.

"If you're a child molester, there's no cure," he said. "They can't stop you. Pathological? There's no cure."

"How stupid are the people of Iowa?" Trump asked at Iowa Central Community College on Thursday night, according to The Associated Press. "How stupid are the people of the country to believe this crap?"

But the former "Apprentice" star's anger was not limited to Carson. Trump also slammed Carly Fiorina, a former Hewlett-Packard chief executive, who has had strong performances in the last two GOP presidential debates, sponsored by business stations CNBC and Fox Business Network, respectively. At one point, Trump referred to his challenger as "Carly whatever-the-hell-her-name-is," The Washington Post noted.

The billionaire also used his appearance to tackle immigration, one of the key issues of his presidential bid, the newspaper said.

"If you cross the United States border illegally, you get a job, you get a driver's license ... you get food stamps, you get a place to live, you get health care, housing, child benefits and in many cases education," he contended.