Sen. Marco Rubio went after businessman Donald Trump about a class-action lawsuit against his entrepreneurship institute Trump University, pushing forward his argument that the front-runner is a “con artist” that defrauded students.

“That’s why Trump University is so relevant here,” the Florida Republican said. “People borrowed money and they signed up for this fake university. And these people owe all of this money now and got nothing in return for it. But you were willing to say whatever you had to say to get them to give you their money.”

Trump pushed back, arguing that the lawsuit is a civil case he could have settled “very easily,” but he doesn’t settle easily when he’s right.

“Ninety-eight percent approval rating, we have an A from the Better Business Bureau, and people like it,” Trump said. “We have a situation where we will win in court. Many of the people, the witnesses, did tremendously and made a lot of money by taking the course.”

Rubio cut in, disputing Trump’s facts: “You got a D minus.” Fox News’s Megyn Kelly also jumped in, pointing to reports that the university’s most recent rating was a D minus when it was last publicly available.

Shortly after the exchange, the Better Business Bureau’s website crashed.

The relevant portion starts at about 6:40 in the video.

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