Trump, for his part, said that he would "absolutely" get rid of Obamacare, but that he would keep in place law that requires insurers to cover individuals regardless of preexisting conditions. He also said that allowing insurers to compete across state lines –– an idea long championed by many reform advocates –– would foster competition and reduce prices.

Pressed by a moderator on how the preexisting conditions provision could be maintained without an accompanying mandate for healthy people to buy insurance, Trump insisted that that wasn't the case.

"I think they're wrong 100 percent," he said. "What we need — look, the insurance companies take care of the politicians. The insurance companies get what they want. We should have gotten rid of the lines around each state so we can have real competition."

Trump continued to talk about the "lines" around each state, and saying that insurance companies were "making a fortune," which served as an opening for Rubio.

"Here's what you didn't hear in that answer, and this is important guys, this is an important thing," he said. "What is your plan? I understand the lines around the state, whatever that means. This is not a game where you draw maps."

The two men quickly began a back-and-forth, talking over each other, with Rubio repeatedly asking Trump for his plan and Trump repeatedly mentioning the lines between the interruptions.

Finally, said the real estate mogul: "You get rid of the lines, it brings in competition. So, instead of having one insurance company taking care of New York, or Texas, you'll have many. They'll compete, and it'll be a beautiful thing."

Rubio concluded: "So, that's the only part of the plan? Just the lines?"