The party’s candidate, a billionaire businessman with no political experience, refused to apologise over comments about the wife of Jeb Bush, saying he said nothing wrong.
“No, I won’t do that because I said nothing wrong, but I do hear she’s a lovely woman.”
And he was on the receiving end when Carly Fiorina drew huge applause facing up to his recent jibe over her looks.
Fifteen republicans are vying to be the party’s White House nominee in 2016.
The debate was hosted by CNN.