Billionaire also dangles prospect of third-party run over ‘unfair’ treatment by national committee, saying it is in violation of pledge agreed with candidates

Republican frontrunner Donald Trump has threatened to sue Ted Cruz over the senator’s eligibility for president, saying that unless his rival stops telling “lies” he will take the issue of his birth in Canada to court.

With less than a week to go until the next Republican primary contest in South Carolina, Trump also lashed out at party leaders, making a veiled threat to run a third-party campaign. The warning came in response to Trump’s complaint that he had been booed during Saturday night’s debate because the audience had been stuffed with wealthy donors who opposed his maverick run.

Trump heaped insults on Cruz in both the press conference and statement, calling the Texas senator “a totally unstable individual”, “a basket case” and “unhinged”.

In a simultaneous statement released by his campaign, Trump said: “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.”

Cruz, who beat Trump in the Iowa caucuses earlier this month, “is lying with the hopes that his statements will go unchecked until after the election and he will save his failing campaign”.



“I learned so much from Iowa and that somebody could be so dishonest,” Trump said, referring to tactics by Cruz’s campaign in the state. Hours before the caucuses, Cruz staffers called homes to say, falsely, that opponent Ben Carson had quit the race and Iowans should support Cruz instead. The campaign also posted official-looking flyers on people’s homes that listed neighbors and gave invented “voter violation” grades.

Cruz apologized to Carson over the tactics, but Carson has refused to comment. His campaign later turned recordings of the calls into campaign ads.

Earlier on Monday, the billionaire hinted he may still run an independent campaign for president, despite a pledge he signed last year to stay within the party.

Trump, who was booed at a debate on Saturday, complained that the audience was full of “lobbyists and donors” whom he accused of manipulating his rivals. “Those tickets were all special interest people. I know ’em,” he said.



“I signed a pledge but it’s a double-edge pledge, and as far as I’m concerned they’re in default of the pledge.”

A spokesman for the Republican National Committee told the Guardian: “The language of the pledge is pretty straightforward.”

The pledge, he said, “simply states the candidates pledge to run as a Republican and support the nominee. Nothing more and nothing less.”

The men and women in the audience were largely at the candidates’ discretion, according to the RNC: “Each candidate received 100 tickets which is the largest amount so far. The candidates as a whole were the largest group of ticket holders.”

But Trump declared said “the pledge isn’t being honored by them”, without elaborating on what the Republican party’s obligations would be under the agreement. He said the debate was “a disgrace” and “the RNC does a terrible job”.

In the past two debates, audiences booed Trump repeatedly after tangling with a rival, Jeb Bush, on issues like the Iraq war and eminent domain. The Trump campaign has insisted that the audiences were packed with “donors and special interests”, a claim that has been repeatedly and vehemently denied by party leadership in the RNC.

Trump did elaborate on how he noticed familiar faces out in the crowd, and mimicked how one acquaintance waved and sniggered. “He’s going ‘boo, boo!’ And he’s waving at me,” Trump said. “They’re booing me because they’re having fun!”

“I’m saying this is crazy! But I know many of these people,” he continued. “That was a wealthy room.”



The billionaire has made his independence from lobbyists and donors a central pillar of his campaign, though his claim of a completely self-funded campaign is freighted with half-truths and caveats. Trump has nevertheless accused his rivals, all active politicians for years and sometimes decades, of being at the beck and call of special interests such as Wall Street and the oil companies.

Trump’s threat to run as a third-party candidate is unusual since it comes five days before the South Carolina primary – a state where the Republican frontrunner has a commanding lead in the polls and is expected to win easily.

In his anti-Cruz statement, Trump runs through various accusations levelled by the senator and attempts to rebut them. “What Cruz says is incredible,” he told reporters. “I will bring that lawsuit if he doesn’t apologize.”

Trump raised Cruz’s birthplace repeatedly before the Iowa caucuses, and cited the opinion of a Harvard Law professor who claims Cruz’s eligibility is an “unsettled” question. Cruz has argued that he is eligible, as was John McCain, who was born in the Panama Canal Zone to two Americans. In 2008 the Senate passed a resolution confirming McCain’s eligibility, but McCain himself has said Congress should examine Cruz’s status.