Fox News host and debate moderator Megyn Kelly, who has had a tumultuous history with Trump, made sure to bring up "the elephant not in the room" -- and the other candidates jumped at the opportunity to bash the business mogul.
Rival GOP candidate Ted Cruz even did an impression of Trump, mocking the former Celebrity Apprentice host's bombastic personality.
"I'm a maniac and everyone on this stage is stupid, fat and ugly," the Texas senator yelled, doing his best impersonation.
Jeb Bush also managed to get in a few jokes, saying, "I kinda miss Donald Trump. He was a little teddy bear to me. We always had such a loving relationship there in these debates and in between with the tweets. I kinda miss him. I wish he was here."
While the debate continued on, Trump hosted a rally at nearby Drake University, where the primary candidate raised money for Wounded Warriors and a number of veterans' organizations.
On Tuesday, Trump announced that he would be skipping the final showdown between the Republican presidential hopefuls, citing his acrimonious relationship with Fox News, which hosted the sanctioned debate.