"He's a clown," Rubio said during an appearance on Fox News after host Bret Baier played a clip of Trump's insults at a campaign rally earlier in the day.
"Look, I saw him back stage. He was nervous, he was waving his arms around," Rubio continued, referring to the debate the previous night. "I think it is time to take the mask off of this guy."
Rubio went off on Trump's business record: "He is a guy that portrays himself as defender of the little guy in this country. He has been exploiting working Americans for 40 years."
"When his businesses went bankrupt, the first people who didn't get paid were those small contractors," Rubio said. "He had people that put their confidence in him, signed up for Trump University. Some of them paid $35-36,000 and they got nothing for it because they trusted in his name and got stuck."
Rubio's characterization of Trump as a "clown" came after the businessman called him a "lightweight," "nervous basket case" and "a little frightened puppy."
Trump unleashed new endorsement New Jersey Gov. Chris Christie to go after the Florida senator in the increasing war of words.
"Marco Rubio, your campaign is almost over, buddy," Christie said during a rally in Oklahoma City before introducing Trump to the stage, suggesting Rubio was "showing a lot of desperation today."
"Donald Trump represents strength, and Marco Rubio represents Washington, D.C."