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Donald Trump again threatened to sue Ted Cruz over whether he's eligible to run for president

The billionaire businessman and the Texas senator have been fighting in South Carolina, where they both hope to win in Saturday's primary

CNN  — 

Donald Trump said Tuesday he is “very seriously” thinking about filing a suit to challenge Ted Cruz’s eligibility to be president.

Trump’s threat of litigation, which the billionaire businessman has recently brought up several times in recent days, came during an interview on ABC’s “Good Morning America” on Tuesday, when he was pressed by host George Stephanopoulos over whether he would follow through with the suit against Canada-born Cruz’s presidential qualifications, as Trump has suggested he might.

Trump replied, “I’m thinking about it very seriously George, I already have a lawyer, we’re looking at it very seriously, we’re thinking about it.”

“He was born in Canada, lived there for years, and then under that period … you know, you take a look at this,” Trump said, adding later, “When you talk about a natural born citizen, according to many great lawyers, I’ve been looking at very strongly over the last week.”

The threat to sue came amid a flurry of attacks on the Texas senator, who has thus far mounted the most serious primary challenge to the current GOP front-runner, and whom Trump continued to accuse of dirty campaigning and lying about his positions on the Second Amendment and Obamacare.

RELATED: Cruz ad paints Trump as unprincipled

Cruz and his campaign responded to Trump’s attacks Monday by dismissing the billionaire businessman and saying he’s lashing out in ager.

“To be fair to Donald, he doesn’t know what he actually believes so he can’t really be expected to defend himself with reason and facts,” said Rick Tyler, Communications Director for the Cruz campaign.

Trump said Tuesday his issue with Cruz is what he sees as his dishonesty.

“Let me just say, I’ve dealt with many people over my lifetime, and I’ve been very successful, and I’ve dealt with some people a lot tougher than him, but I’ve never dealt with anybody that lies like him,” Trump charged.

“Ted Cruz is a liar, I mean he really just outright lies,” he continued. “He’ll say whatever he wants to say. I actually think he’s a very unstable person, I really believe that. I think he’s a very unstable person. But I’ve never had somebody take something that you believe in and just say the exact opposite.”