GREENVILLE (South Carolina) • The Republican presidential race veered into vicious personal attacks over the weekend as White House hopefuls brawled in their latest debate, with front-runner Donald Trump and Mr Jeb Bush locking horns in some of the campaign's most pointed clashes to date.

Saturday's showdown, the ninth of the months-long battle for the Republican nomination, began with a respectful moment of silence for iconic conservative US Supreme Court justice Antonin Scalia, who had died suddenly earlier that day.

But with a primary just one week away in South Carolina, a state where national politics often gets dragged into the mud, the debate in Greenville quickly turned nasty and divisive, with billionaire Trump, former Florida governor Bush, and Senator Ted Cruz exchanging heated verbal blows.

Having helped raise more than US$155 million (S$216.7 million), and with his family's political reputation on the line, Mr Bush - after poor showings in New Hampshire and the Iowa caucuses this month - had the look and feel of a man taking his last, best shot to rescue his candidacy and destroy Mr Trump's.

He questioned Mr Trump's knowledge and readiness to confront national security threats, noting that Mr Trump had made positive remarks about Russia's role in fighting the Islamic State in Iraq and Syria (ISIS) group.

"It is absolutely ludicrous to suggest that Russia could be a positive partner in this," Mr Bush said.

"Jeb is so wrong; Jeb is absolutely...," Mr Trump started, before being cut off by boos from the audience. "You have got to fight ISIS first," he added. "You have to knock them off strong."

Moments later, Mr Trump stood by his past remarks that he would have supported the impeachment of former president George W. Bush over the 2003 invasion of Iraq, saying that administration misled the country about weapons of mass destruction.

"They lied, they said there were weapons of mass destruction, and there were none," Mr Trump said.

His remarks drew a quick attack from the former president's brother - Jeb - who is well aware that many South Carolina Republicans hold high opinions of Mr George W. Bush as well as of their parents.

"I'm sick and tired of him going after my family," Mr Bush said. "My dad is the greatest man alive, in my mind. My mum is the strongest woman I know."

Mr Trump shot back: "She should be running."

The real estate mogul also appeared on the verge of losing his cool when Mr Cruz invoked Mr Scalia's death to warn that Mr Trump would appoint "liberals" to the Supreme Court and brought up the billionaire's past support for abortion rights.

"You are the single biggest liar," Mr Trump said, glaring at Mr Cruz.

It was an extraordinary back-andforth on the national stage, with candidates often ignoring the moderators and going after one another. "We are in danger of driving this into the dirt," one of the CBS debate moderators said at one point.

Mr Cruz and Mr Trump have the first two nomination contests in Iowa and New Hampshire under their collective belt, with Mr Cruz winning Iowa and Mr Trump - who now holds a substantial lead in South Carolina - winning New Hampshire.

The Republican field has narrowed to six candidates, including retired neurosurgeon Ben Carson and Senator Marco Rubio of Florida.

Mr John Kasich, who placed an impressive second in New Hampshire, has sought to portray himself as the most reasonable and centrist of the candidates. He told the group at one point: "I think we are fixing to lose the election to Hillary Clinton if we don't stop this."

The state holds its Republican primary on Saturday, the same day Democrats vote in Nevada for either Mrs Hillary Clinton or Senator Bernie Sanders.

AGENCE FRANCE-PRESSE, NEW YORK TIMES