DORCHESTER, S.C. -- For the first time Thursday night, Ted Cruz will stride onstage for a presidential debate under a cloud. Donald Trump has been hammering the Canada-born senator's eligibility to serve as president.
The dynamics at the seven-man debate in Charleston will be complex. Cruz and Trump are girding for battle. Yet they stand apart from the other five Republican contenders, Marco Rubio, Jeb Bush, Chris Christie, John Kasich and Ben Carson. All but Carson are vying to emerge as the establishment-approved alternative. Rubio and Cruz have sparred, as have Bush and Rubio.
But the Cruz-Trump relationship has been so friendly for so long, an eruption would be dramatic. They can't both emerge as the nominee, and with less than three weeks before the Iowa caucuses, they've each become more belligerent over the issue of whether Cruz's Canadian birth makes him ineligible to be president.
Cruz, discussing the issue after a rally here, telegraphed how he would respond.
"The merits of this issue are straightforward," he said, citing as usual John McCain, George Romney and Barry Goldwater, all candidates for president born outside U.S. turf. "This issue did not seem to concern Donald until a little over a week ago, when suddenly, he was trailing in the polls in Iowa. And I understand Mr. Trump and other candidates in the race being disturbed that conservatives are coming together."
His handling of the issue in the debate, one of just two remaining before Iowa kicks off the voting Feb. 1, foreshadows an increasing hurdle for Cruz _ how to deal with Trump.
Given the attacks, he would look weak if he continues to embrace and affirm Trump as a fellow champion for the public's anger at Washington. Some Republicans are eager for Cruz to clobber Trump as a crony capitalist, erstwhile supporter of abortion rights, a sexist, bigot and a poor businessman. But candidates who have gone down that path have little to show for it, including Jeb Bush, who trails badly, and Rick Perry, who was forced out of the race months ago.
Trump has been playing "Born in the USA" at rallies to needle Cruz. He reminded one crowd this week that Cruz "was actually a citizen of Canada until 15 months ago. ... It's a real problem." On Wednesday, he even urged Cruz to quit.
Cruz finally fired back. He suggested a better theme song for his rival: "New York, New York, because Donald comes from New York and he embodies New York values."
Apryll Gill, 39, an accountant from Summerville, S.C., said she's comfortable with Cruz's eligibility but, like many of his backers, doesn't expect the issue to fade by itself.
"Trump is trying to stir up paranoia. It's a concern. Those fears need to be quelled," she said.
The latest Iowa Poll, released Wednesday by the Des Moines Register and Bloomberg, showed Cruz slipping. His 25-22 lead over Trump is a statistical tie, given the poll's margin of error. That's a big drop from a month ago, when he enjoyed a 31-21 lead.
It's unclear whether the birther attacks are to blame; 1 in 8 Iowans said Cruz's birth in Canada "bothers" them, enough to make a difference in a close race.
If Cruz or another candidate can't win there, Trump could become a juggernaut. He's already on top in New Hampshire, and winning both states could make him unstoppable.
His needling prompted Cruz to abandon a long-standing policy of refraining from criticism. Cruz even held his tongue as others denounced Trump's call to round up and deport millions of people in the country illegally, or to bar all Muslims from entering the country. The tactic served him well, as he rose to within striking distance and then pulled ahead in Iowa.
In Dorchester, airline supervisor Jared Peterson, 41, said Cruz would be smart to stick to the high road.
"Trump's trying to cause a little stir. Cruz is trying to elevate the conversation. We've had enough bickering in the country," he said.
Cruz insists the issue of his eligibility is a matter of settled law. A growing chorus of legal experts disagree on whether it's settled, though most generally agree that Cruz is eligible by virtue of his mother's citizenship, which made him an American from birth.
But the Constitution requires a "natural born citizen," traditionally thought to mean birth on U.S. soil.
One legal precedent Cruz cites is shaky: A 1790 act of Congress providing that offspring of American citizens born outside U.S. territory would be deemed "natural born citizens." That ignores a law enacted five years later.
The 1795 Naturalization Act, as pointed out by Mary Brigid McManamon, a professor at Wiedener Law School in Delaware, stated that offspring would henceforth be deemed "citizens," stripping the "natural born" phrase that echoed Article 2 of the Constitution _ the part that defines eligibility for president.
This is both a legal and a political headache.
On the legal front, Cruz survived a ballot challenge in New Hampshire when a state ballot commission ruled it has no authority to pass judgment on the issue. A lawsuit is pending in Vermont. Some legal scholars predict that once the first votes are cast next month, no court in the land would be willing to intercede, because that would disenfranchise all the Iowans and New Hampshirites who voted for Cruz.
As a political issue, the attack has put Cruz on the defensive for more than a week.
Other candidates have begun piling on. Mike Huckabee told Bloomberg Politics on Wednesday the issue "should give everybody a little concern." Rick Santorum said Cruz's eligibility "is not settled law."
And Public Policy Polling, which also sees a virtual tie in Iowa between Cruz and Trump, found in a survey released Tuesday that nearly half of Iowans don't think someone born in another country should be allowed to serve as president.