NORTH CHARLESTON, S.C. — Donald Trump and Sen. Ted Cruz of Texas sharply and at times comically attacked each other Thursday night over the Canada-born Cruz's eligibility to be president, shedding months of cordiality as the latest Republican presidential debate became a hand-to-hand fight in their razor-close contest in the Iowa caucuses.
Cruz, who has gained ground against Trump recently in Iowa, where they are now virtually tied, charged that Trump was turning desperate because his standing as the leader of the Republican field had turned shaky. Cruz, who for months was Trump's chief defender and closest ally in the race, noted that Trump had not joined others in the fall in trying to make an issue out of Cruz's American mother's giving birth in Calgary, Alberta.
"The Constitution hasn't changed, but the poll numbers have," Cruz said. "Donald is dismayed that his poll numbers are falling in Iowa." Cruz added that the law was on his side, noting that Sen. John McCain, while born in Panama, was eligible to run for president. By Trump's standard, Cruz asserted, Trump himself might not be eligible to run for president because his mother was born in Scotland.
"But I was born here — big difference," Trump said.
The ferocious back-and-forth marked the unmistakable end of the de facto non-aggression pact between the two leading candidates, presaging a new phase of the campaign in which the two hopefuls winning support from hard-line conservatives can be expected to increasingly turn their fire on each other.
It was Cruz's most aggressive performance in the six Republican debates so far as he sought to protect the political support he has built among social conservatives and evangelical Christians. He was relentless in trying to put Trump in his place, a move aimed in part at appealing to establishment Republicans who are deeply uncomfortable with Trump's candidacy and whom Cruz has started to court.
For several moments, the debate turned from a reality show into a comedy as Trump mused that if he chose Cruz as his running mate, Democrats would sue to challenge Cruz's eligibility — as they would if Cruz won the presidential primary.
"If you become the nominee, who the hell knows if you can even serve in office?" Trump said.
Cruz, a pugnacious, polished debater as a Princeton undergraduate, gave no quarter.
"I'm not going to take legal advice from Donald Trump," he said to laughter. And he offered to make Trump his running mate, so he could assume the presidency if a theoretical legal challenge against Cruz's eligibility were successful.
Sen. Marco Rubio of Florida, seeing an opening to position himself above the spat, eventually interjected, mocking his rivals.
"I hate to interrupt this episode of Court TV," he said, drawing laughs and applause. He then sought to refocus the conversation on President Barack Obama's shortcomings and what he said was a need to revive the country, safe terrain for Republican primary voters.
Cruz, too, tried to rise above the fray by repeatedly attacking the president, decrying Obama's omission from the State of the Union speech on Tuesday any mention of the Navy sailors who were temporarily detained by Iran this week. "It was heartbreaking, but the good news is, the next commander-in-chief is standing on this stage," Cruz said.
At first, his other rivals joined in, trying to keep the focus on Obama and Hillary Clinton.
"On Tuesday night, I watched story time with Barack Obama, and it sounded like everything in the world was going amazing," said Gov. Chris Christie of New Jersey, who said that U.S. alliances were in bad need of repair and that adversaries needed to understand "the limits of our patience." He also said Cruz was right in calling Obama to account for not mentioning the face-off with Iran.
Former Gov. Jeb Bush of Florida said Obama was living in an "alternative universe" in which the Islamic State militant group was not a lethal threat to America, terrorism was being contained, and China and Russia were not on the rise. "American leadership in the world is required for peace and stability," he said.
The candidates also sought to find provocative new ways to tar Clinton.
"If she gets elected, her first 100 days, instead of setting an agenda, she might be going back and forth between the White House and the courthouse," Bush said, drawing applause.
Rubio sought to top that. "I would go, first of all, one step further," he said. "She wouldn't just be a disaster. Hillary Clinton is disqualified from being commander-in-chief of the United States." Over applause, Rubio continued, "Someone who cannot handle intelligence information appropriately cannot be commander-in-chief, and someone who lies to the families of those four victims in Benghazi can never be president of the United States."
Undercard debate: Ahead of the main debate, a preliminary forum among trailing candidates featured just three: former Hewlett-Packard Chief Executive Carly Fiorina, former Pennsylvania Sen. Rick Santorum and former Arkansas Gov. Mike Huckabee. Kentucky Sen. Rand Paul opted against participating after failing to meet criteria to remain in the main debate.
Fiorina asserted that unlike the other woman running, Hillary Clinton, "I actually love spending time with my husband."
Santorum cast his plan to deport people in the U.S. illegally as a way to "export America."
"They learned the English language. They learned about capitalism. They learned about democracy," he said. "You want to stop the flow of immigrants? Let's send 6 million Mexicans, Hondurans, Guatemalans, El Savadorians back into their country, so they can start a renaissance in their country so they won't be coming over here anymore."
Huckabee criticized Obama for new executive actions designed to subject more gun sales to background check requirements, while questioning the president's commitment to defeating Islamic State.
"We have a president who seems to be more interested in protecting the reputation and image of Islam than he is protecting us," he said.
Information from Tribune News Service was used in this report.