Ben Carson, newly minted frontrunner for the Iowa Republican presidential caucus, is pushing back against criticism from billionaire Donald Trump that he is "super low energy."
"I don't get into the mud pit," Carson, a retired neurosurgeon, said in a partial transcript of an interview with NBC's "Meet the Press" made available by the network ahead of Sunday's broadcast.
Trump, 69, a real estate mogul and reality TV star, has spent several months leading a large pack of Republican hopefuls in opinion polls.
Two recent surveys, the Quinnipiac Poll and the Bloomberg Politics/Des Moines Register Iowa Poll , showed Trump falling behind Carson in Iowa, where the first ballots of the 2016 presidential race will be cast on Feb. 1.