Republican presidential candidates Ted Cruz was forced to defend himself from a crossfire of attacks by Donald Trump and Marco Rubio in a pair of South Carolina town halls Wednesday night.

Appearing on CNN, Cruz said he "laughed out loud" when he received a cease-and-desist letter from the Trump campaign that threatened a lawsuit over a Cruz ad questioning Trump's record on abortion. The ad features footage of a 1999 interview in which Trump says he's "very pro-choice."

"I don't think anyone is surprised that Donald is threatening to sue people," Cruz told moderator Anderson Cooper. "He's done that most of his adult life."

"In any defamation case, truth is a complete defense," added Cruz, whose feud with the real estate billionaire escalated this week after Trump threatened to sue the Canada-born Cruz over his eligibility to run if Cruz did not "take down his false ads and retract his lies."

Appearing in his own town hall on MSNBC, Trump slammed Cruz as "a nasty guy."

"He doesn't have one Republican endorsement from the Senate and he works with the Senate," Trump said. "Think of it. Hard to believe." Cruz addressed his relationships with his Senate colleagues in response to an audience question Wednesday.

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"I'll tell you why they say Ted is unlikable in Washington," Cruz said. "Because I'm actually honoring the commitments that i made to the men and women who elected me."

Rubio, trying to rebound in South Carolina after a disappointing fifth-place finish in the New Hampshire primary, again accused Cruz of dishonesty about the Florida senator's position on amnesty for illegal immigrats.

"He's been lying," Rubio said. "If you say something that isn't true and you say it over and over again, and you know that it's not true, there's no other word for it."

Rubio, who was endorsed by South Carolina Gov. Nikki Haley earlier Wednesday, also assaulted Cruz's campaign tactics. He accused Cruz supporters of using "push polls" and creating a fake Facebook page wrongly claiming that Rep. Trey Gowdy, R-S.C. had switched his endorsement from the Florida senator to Cruz.

Cruz denied being involved with anything untoward and called for anyone with evidence to come forward.

Trump and Rubio are "repeatedly putting forth fabrications with no evidence, no basis whatsoever, just trying to throw mud and attack," Cruz said. "The insults and the falsehoods and the fabrications have no business in politics. It is incumbent upon all of us to speak the truth."

The Associated Press contributed to this report.