GREENVILLE, South Carolina (Reuters) - Republican presidential candidates Donald Trump and Jeb Bush engaged in an angry clash on Saturday (Feb 13) over the Iraq war and the proper United States role to take against Russia's involvement in Syria.
Mr Trump, leading polls in South Carolina and in position to take command of the Republican nomination fight if he wins the state's Republican primary on Feb 20, attacked Mr Bush's brother, former President George W. Bush, for invading Iraq in 2003 over weapons of mass destruction that were never found.
The raucous back-and-forth was the most bitter exchange between the two men over the course of nine debates and was a sign of how critical both see a strong showing in South Carolina.
"George Bush made a mistake," Mr Trump thundered. "We all make mistakes. But that one was a beauty... They lied! They said there were weapons of mass destruction. And there were none."
As many in the crowd booed Mr Trump, the billionaire Republican front-runner dismissed them as "lobbyists and special interests" who supported Mr Jeb Bush, the former Florida governor.
Mr Bush also criticized Mr Trump for remarks praising Russian President Vladimir Putin, saying Mr Putin is stirring turmoil in Syria by launching air strikes in support of Syrian President Bashir Assad, who Washington would like to leave power.
Mr Bush, who will campaign on Monday with his brother George, rejected Mr Trump's comments and defended his family. "I'm sick and tired of him going after my family," Mr Bush said. "My dad is the greatest man alive in my mind. While Donald Trump was building a reality TV show, my brother was building a security apparatus to keep us safe. And I'm proud of what he did."
"He had the gall to go after my mother," Mr Bush said, reminding the audience that Mr Trump had criticised his 90-year-old mother Barbara Bush, wife of former President George H.W. Bush. "My mother is the strongest woman I know."
"She should be running," Mr Trump responded.
Mr Bush provoked another outburst from Mr Trump by saying the Republican nominee should be someone "who doesn't brag, for example, that he has been bankrupt four times."
"That's another lie," said Mr Trump. "I never went bankrupt."
The Bush campaign laid into Mr Trump for criticizing his family.
"I'm sick and tired of Trump attacking my family. This isn't about my family or his family. It's about your family. #GOPDebate," Mr Bush's official account (@JebBush) tweeted during the debate.
The hashtag #GOPDebate was the top-trending item on Twitter Saturday night.
Mr Trump dominated the bulk of the conversation in the first half, with 42 per cent of the mentions associated with the hashtag #GOPDebate, according to Twitter data.
Mr Bush was a distant second, with 23 per cent of the conversation.
The New York billionaire also had a heated exchange with Senator Ted Cruz when the senator said Mr Trump would appoint liberals to the Supreme Court.
"You are the biggest liar," Mr Trump said sharply.
As they tried to talk over each other, Sen Cruz chided Mr Trump by saying: "Adults don't interrupt."
Ohio Governor John Kasich, who finished second in the New Hampshire primary last Tuesday and who pushes an optimistic message, called for calm.
"These attacks, some of them are personal. I think we're fixing to lose the election to (Democratic front-runner) Hillary Clinton," he said.
Mr Trump's attacks on the Bush family carried risks for him, since many US military veterans in South Carolina have long supported the family.
Sen Cruz and Senator Marco Rubio renewed their battle over who is the toughest on illegal immigration with Sen Cruz insisting that Sen Rubio, as part of a Gang of Eight senators who sought a compromise on legislation in 2013, was for "amnesty" but now is against it for political purposes.
He insisted that Sen Rubio had said in Spanish on Univision that he would not rescind an executive order signed by President Barack Obama in support of the children of illegal immigrants.
Sen Rubio shot back: "I don't know how he knows what I said on Univision because he doesn't speak Spanish."
As the crowd roared, Sen Rubio said Sen Cruz is "telling lies... He's lying about all sorts of things and now he makes things up".
The death of Supreme Court Justice Antonin Scalia also loomed large over the debate, with over 9,000 mentions during the first half, according to social media analytic firm Brandwatch.
Before the clashes broke out, the Republican candidates urged President Barack Obama not to nominate a successor to Justice Scalia, saying it should be up to the next president to decide.
Justice Scalia's death, announced earlier on Saturday, and the consequences for the conservatives' 5-4 advantage on the high court cast a shadow over the ninth debate between rivals for the Republican presidential nomination for the Nov 8 election.
"I would like the President for once here to put the country first," Ohio Governor John Kasich said at the outset of the two-hour debate hosted by CBS. "We're going to have an election very soon... I think we should let the next president of the United States decide."
Mr Obama, speaking shortly before the debate began, said he planned to nominate a successor to Justice Scalia and said the US Senate should give the nominee careful consideration.
The Republican candidates were unanimous in saying Mr Obama should put off a decision.
Mr Trump said Senate Majority Leader Mitch McConnell should ensure that any Obama nominee is blocked from confirmation. "Delay, delay, delay," Mr Trump said.