While Donald Trump is still by far the first choice of Republican voters, other contenders have been gaining ground on the outspoken billionaire.
Fox News presenter Bill O'Reilly asked Mr Trump if he needed to be kinder and more mature.
"I think I'm a nice person, I have great relationships," he responded.
The question came after Mr Trump called Florida Senator and fellow Republican nominee candidate, Marco Rubio, a "clown".
Mr Rubio, who is making gains in the polls, in-turn called Mr Trump's campaign a "freak show".
"I don't really know him," Mr Trump told Fox. "All of a sudden he attacks me about nothing."
Watch the video for the full CBS report.