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Donald Trump threatens to sue Ted Cruz over his Canadian birth

Last Updated Feb 15, 2016 7:03 PM EST

Business mogul Donald Trump was in the midst of a fiery press conference in Hanahan, South Carolina Monday, berating Texas Sen. Ted Cruz, when reporters' phones suddenly started buzzing.

A Trump press release appeared, with the subject line, "Donald J. Trump Responds to the Lies of Senator Cruz and Warns of Legal Action."

"Ted Cruz is a totally unstable individual," the statement began.

"He is the single biggest liar I've ever come across, in politics or otherwise, and I have seen some of the best of them. His statements are totally untrue and completely outrageous," Trump's press release continued. "It is hard to believe a person who proclaims to be a Christian could be so dishonest and lie so much."

Last August, Trump had this to say in a television interview with NH1: "I like Ted Cruz." But times change. Now, Trump is threatening a lawsuit against Cruz.

"One of the ways I can fight back is to bring a lawsuit against him relative to the fact that he was born in Canada and therefore cannot be President," the statement said. "If he doesn't take down his false ads and retract his lies, I will do so immediately. Additionally, the RNC should intervene and if they don't they are in default of their pledge to me."

Trump was responding to the latest round of Cruz attacks, which have, in turn, grown more vicious. Cruz has called Trump's sister, Maryanne Trump Barry, a federal judge for the U.S. Court of Appeals for the Third Circuit, "a radical pro-abortion extremist."

In 2000, Trump's sister wrote a majority opinion that struck down a ban on late-term abortions. In his statement, Trump said, "Cruz said I would be appointing a liberal judge, when in fact I will appoint a great conservative and I am the only candidate who has gone so far, at the debate, as to suggest two individuals I feel would best represent the conservative values we need to protect: William "Bill" Pryor Jr. and Diane Sykes."

At the press conference, a riled Trump expressed dismay that Cruz would go after a family member. "Can you imagine? My sister," Trump said. "I think first of all my sister has nothing to do with me. She's a federal judge at a high, high level....a highly brilliant woman. Known as a brilliant judge. I don't even know what her views are. I don't think she'd want to tell me."

Trump, too, has mentioned the relatives of his opponents. When Jeb Bush brought his mother, former First Lady Barbara Bush, on the campaign trail, Trump derisively referred to her as "mommy," though that was a slap more at Jeb Bush, than at his mother.

The billionaire continues to lead his opponents -- according to the latest CBS battleground tracker in South Carolina, Trump is nearly outperforming his three closest competitors combined.

"Now [Cruz will] apologize, but I don't want an apology after the election," Trump said at the press conference. "I want the apology before, and if he doesn't, I'm going to bring a lawsuit, because in my opinion based on what I've learned over the past two, three days from very top lawyers, he doesn't even have the right to serve as president or even run as president. He was born in Canada, so I will bring that lawsuit if he doesn't apologize."

At an earlier event in Mt. Pleasant, Trump called Cruz "unstable" and "nuts" and referenced a Cruz meeting a few months ago with a small group of loyalists in New York.

"Take a look at Ted Cruz's donors," Trump goaded the room. "Take a look at what he said about gay marriage when he was in the law offices in Manhattan, and what he said under a microphone when he didn't know the microphone was working, or somebody had their cellphone on." Trump was referring to Cruz's answer in that meeting to a question about whether fighting same-sex marriage would be a top-three priority. Cruz reportedly responded "No."

Trump, as he has many times before, also floated a third party run. He told the audience that the party had "defaulted" on its end of the pledge to treated him fairly.

Cruz, for his part, responded to Trump's press conference at one of his own in Camden, South Carolina - saying that Trump had "apparently lost it" and that his rising poll numbers had "rattled" Trump.

The South Carolina primary is on Saturday, leaving five days for the race to get still uglier.