Diatribes between Republican presidential candidates Donald Trump and Jeb Bush on the Iraq war, the Bush family, and Trump's business dealings dominated a debate which saw fierce competition for a good showing at the first primary in the country's south.
The candidates clashed heavily on Saturday in a two-hour debate in South Carolina, underscoring the importance of the state's vote in a week.
Leading in the polls, Trump came under sustained fire from his rivals seeking to emerge as the main anti-Trump alternative.
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Trump attacked Jeb Bush's brother for launching the Iraq war in 2003, calling it a "big, fat mistake", in the most bitter exchange yet between the two in a debate before the November 8 presidential elections.
"George Bush made a mistake," Trump said. "We all make mistakes. But that one was a beauty ... They lied! They said there were weapons of mass destruction. And there were none."
Many in the crowd booed Trump and in response he dismissed them as "lobbyists and special interests" who supported Jeb Bush, the former Florida governor.
Bush also criticised Trump for remarks praising Russian President Vladimir Putin, saying Putin is stirring turmoil in Syria by providing military support to Syrian President Bashir Assad, who Washington would like to leave power.
Bush, who will campaign on Monday with his brother George, rejected Trump's comments and defended his family.
"I'm sick and tired of him going after my family," 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," Bush added, reminding the audience that Trump had criticised his 90-year-old mother, Barbara Bush, wife of former President George HW Bush.
"My mother is the strongest woman I know."
Bush provoked a response from Trump by saying that the Republican nominee should be someone "who doesn't brag, for example, that he has been bankrupt four times".
"That's another lie," said Trump. "I never went bankrupt."
Trump also had a heated exchange with Ted Cruz when the senator said Trump would appoint liberals to the Supreme Court.
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"You are the biggest liar," Trump said sharply.
As they tried to talk over each other, Cruz chided 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.
Trump's attacks on the Bush family carried risks for him, since many U.S. military veterans in South Carolina have long supported them.
Cruz and Rubio renewed their battle over who is the toughest on undocumented migration. Cruz insisted that 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 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.
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, Rubio said Cruz is "telling lies ... He's lying about all sorts of things and now he makes things up."
| US Republican candidate under fire in debate