When Ted Cruz attacked Donald Trump Saturday night at CBS' Republican primary debate, the bombastic billionaire fired back that Cruz was "the single biggest liar" on the stage.

"For most of his life, [Trump's] policies have been very, very liberal," Cruz said in Greenville, South Carolina. "For most of his life, he has described himself as very pro-choice and as a supporter of partial birth abortions. Right now today as a candidate, he supports federal taxpayer funding for Planned Parenthood. I disagree with him on that."

Trump interrupted and responded with insults.

"You are the single biggest liar," he told Cruz. "You probably are worse than Jeb Bush. You are the single biggest liar. This guy lied -- let me tell you, this guy lied about Ben Carson when he took votes away from Ben Carson in Iowa. And he just continues. And today, I had robo-calls saying that Donald Trump is not going to run in South Carolina' -- where I'm leading by a lot. 'Vote for Ted Cruz.' This guy will say anything. Nasty guy. Now I know why he doesn't have one endorsement from any of his colleagues."

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His rival, however, did not back down, aiming to get in a few more jabs at Trump's conservative record.

"You notice that Donald didn't disagree with the substance that he supports taxpayer funding for Planned Parenthood," Cruz said. "And Donald has this weird pattern. When you point to his record, he screams 'liar, liar, liar.'"

Trump challenged his opponent's claim, asking numerous times, "Where did I support it? Where did I support it, Ted?"

In a 1999 appearance on NBC's "Meet the Press," Trump opposed a late-term abortion ban.

"I'm very pro-choice," Trump had said on the show. And when asked whether he'd ban "partial birth abortions," he said, "No, I would -- I would -- I am pro-choice in every respect, as far as it goes," adding, however, that he hated abortion.

And on funding Planned Parenthood, Trump has said before that "some of the individual things they do are good."

"I know a lot of the things are bad," he said in an interview with CNN in August. "But certainly the abortion aspect of it should not be funded by government, absolutely."

At the debate, Trump defended the organization's other functions, saying Planned Parenthood does "wonderful things having to do with women's health," but "not when it comes to abortion."