Republicans: Senate must block Obama's Supreme Court choice
Republican White House hopefuls have called for US president Barack Obama to step aside and allow his successor to nominate the next Supreme Court justice, following the death of ultra-conservative judge Antonin Scalia.
Only Jeb Bush said Mr Obama had "every right" to nominate a justice during his final year in office.
The former Florida governor said there should be "consensus orientation on that nomination", but added that he did not expect Mr Obama would pick a candidate in that vein.
The five other candidates on the stage in the debate in Greenville, South Carolina, urged the Republican-led Senate to block any attempts by the president to get his third nominee on the court.
"It's up to (Senate majority leader) Mitch McConnell and everybody else to stop it," billionaire businessman Donald Trump said. "It's called delay, delay, delay."
Just six contenders took the debate stage, far from the long line of candidates who participated in earlier Republican events. Yet the Republican race remains deeply uncertain, with party elites still hoping that one of the more mainstream candidates will rise up to challenge right-wingers Mr Trump and Ted Cruz. Many Republican leaders believe both would be unelectable in November.
On the Democratic side, Hillary Clinton told a dinner in Denver, Colorado, that Mr Obama had the right to nominate another justice. He "is president of the United States until January 20 2017. That is a fact my friends, whether the Republicans like it or not," she said.
"Let's get on with it," said left-wing challenger Bernie Sanders, arguing that the Senate should vote on whoever Mr Obama nominated.
Mr Trump and Mr Bush tangled in some of the night's most biting exchanges, highlighting the bad blood between the property mogul who leads the Republican field and the former Florida governor who was once expected to sail to the nomination.
In a particularly heated confrontation, Mr Trump accused Mr Bush's brother, former president George Bush, of having lied to the public about the Iraq war.
"Obviously the war in Iraq was a big fat mistake," Mr Trump said.
Mr Bush, who has been among the most aggressive Republican candidates in taking on Mr Trump, said that while he did not mind him criticising him - "It's blood sport for him" - he was "sick and tired of him going after my family".
Mr Trump was jeered lustily by the audience in a state where the Bush family is popular with Republicans. George Bush plans to campaign with his brother in Charleston on Monday, making his first public foray into the 2016 race.
Candidates used Mr Scalia's sudden death to raise the stakes for the general election.
Mr Cruz cast the moment in stark terms, saying allowing another Obama nominee to be approved would amount to Republicans giving up control of the Supreme Court for a generation.
An uncompromising conservative, Texas senator Mr Cruz urged voters to consider who among the Republican candidates would nominate the most ideologically pure justices.
Saturday's debate comes a week before South Carolina's primary. Mr Cruz and Mr Trump emerged from the first two voting contests with a victory apiece and appear positioned to compete for a win in the first Southern primary.
Ohio governor John Kasich defended himself against attacks on his conservative credentials, particularly his decision to expand Medicaid in Ohio despite resistance from his Republican-led legislature. Mr Kasich argued that his decision was a good deal for the state in the long run.
Mr Bush played the aggressor again, saying that Mr Kasich's actions amounted to "expanding Obamacare" - a deeply unpopular concept among Republicans.
Earlier Vermont senator Mr Sanders used unusually blunt words to express frustration with Mrs Clinton, a former US secretary of state.
"I am really stunned by some of the attacks we are getting from Secretary Clinton," he said.
"Clearly they have been unravelled by the results in Iowa, by our victory in New Hampshire and the progress we are making all over this country."