Ted Cruz and Donald Trump enter Saturday's debate locked in a two-man race for South Carolina, and to prepare, both have gone full negative.

After splitting the first two votes, the New York billionaire has relentlessly hammered away at Cruz on everything from his campaign's tactics to what Trump sees as the Texan's character flaws. And on Friday, Trump warned that he has standing to sue Cruz over questions of his birth and constitutional eligibility to serve in the White House.


“If @tedcruz doesn’t clean up his act, stop cheating, & doing negative ads, I have standing to sue him for not being a natural born citizen,” Trump tweeted of his rival, born in Canada to an American mother.

Asked about the threat, Cruz did not back down. "There's more than a little irony in Donald accusing anybody of being nasty given the amazing torrent of insults and obscenities that come out of his mouth on any given day," he told reporters. "Suddenly every day he comes out with a new attack."

Trump is expected to carry these attacks onto the stage on Saturday at the final candidate forum before South Carolina votes. It’s a fight Cruz’s allies say they are ready for, as they prepare to assault Trump's Republican credentials with an eye on the conservative, religious and security-focused voters throughout the south.

“There’s a Himalayan mountain of evidence out there that Donald Trump is not a conservative,” said Charlie Condon, a former South Carolina attorney general and a Cruz surrogate, pointing to Trump’s past positions on issues including abortion, health care and Wall Street bank bailouts. “I’m confident that everything I’m telling you will be discussed at the Peace Center.”

Condon said that the more Trump attacks Cruz on Saturday, the more the Texas senator will come across as the Trump “alternative.”

“It’s a recognition of what we think the reality is: This is becoming a two-man race,” he said. “So if you’re not comfortable with Donald Trump being president, whether for temperament reasons or judgment reasons or the fact that he really is a campaign conservative—he’s been a Democrat almost his whole life…if you’re uncomfortable with that…Cruz is the alternative.”

Cruz spokesman Rick Tyler said the candidate would be “prepared” for Trump, whose campaign he dismissed as unserious. “This is the Seinfeld candidacy,” he said. “It’s a campaign about nothing.”

The escalation of the conflict between the two leading candidates for the Republican nomination comes as they contest a state that has refined the political dirty trick to a fine art and where the mogul is accusing a “dishonest” Cruz of orchestrating anti-Trump robocalls.

Already, in Iowa, the Cruz campaign came under fire for spreading inaccurate reports that Ben Carson was suspending his campaign on the day of the Iowa caucuses and sending out high-pressure mailers intended to shame inconsistent voters who were likely to support Cruz into turning out.

In South Carolina, where polls show Trump with a double-digit lead over Cruz, the senator and his supporters are not holding back. “I’ve worked campaigns for long time and I’ve never seen the stuff Cruz is putting out,” said one Trump campaign staffer in the state, referring to mailers that question the businessman’s conservative credentials.

According to the Real Clear Politics average, Trump is running a solid first in South Carolina with 37 percent, followed by Cruz at 20 percent. (Marco Rubio sits a distant third at 14 percent.)

“As we approach South Carolina, Trump’s competitors will grow increasingly desperate,” said Seth Weathers, a Trump supporter who briefly served as the businessman’s George state director. “Trump’s tweet was a reminder that he doesn’t take attacks lying down. He never attacks first, but when he responds, he unleashes hell.”