WASHINGTON • Republican White House front runner Donald Trump and nine other 2016 hopefuls will be watched by millions of Americans in their third nationally televised primary debate, as each rival seeks a political opening against the caustic billionaire.
The debate at the University of Colorado in Boulder, due yesterday at 6pm (8am today Singapore time), comes as establishment-leaning candidates struggle to make headway against strong populist currents in their party, although outsider Ben Carson has been nipping at Mr Trump's heels in the polls.
Dr Carson, a retired neurosurgeon and the only African-American in the race, edged ahead of Mr Trump in a new national New York Times/CBS News survey released on Tuesday.
It marked the latest sign of slippage for the real estate tycoon. He could come out swinging against his rivals, particularly Dr Carson whom he has criticised in recent days as a low-energy candidate.
Mr Trump joked at a rally that Dr Carson did not realise he had surged in the polls because he was too busy "sleeping". And he retweeted a post saying that "Gentle Ben is no match for (Russian President Vladimir) Putin or if the truth be told, even for Hillary (Clinton)", the presumptive Democratic nominee.
Dr Carson said on Sunday he would not be dragged into the "mud pit", and his campaign has remained above the fray, highlighting his serious, measured temperament.
A new Gallup poll shows that he has higher favourability ratings than any Republican running.
Dr Carson and Mr Trump draw support from different segments of the Republican electorate, with Dr Carson winning the alle-giance of evangelicals and self-described conservatives.
Mr Trump does better among Republican voters who do not have a college education and with those who are not evangelical.
The two wings of the party also differ on issues ranging from taxes and immigration to gun control and same-sex marriage.
One open question for the debate is whether Mr Jeb Bush, the son and brother of two US presidents, will take Mr Trump's bait. Despite raising mountains of money and starting off as the front runner, Mr Bush has so far failed to set himself apart from the pack.
But one major donor said Mr Bush is taking the long view, expecting the Trump "phenomenon" to fade once voters start paying closer attention to policy specifics.
"He doesn't want to be in this... cesspool of taunts and nonsense."
CNBC, the network telecasting the event, has titled the debate "Your Money, Your Vote", and says it will focus on economic issues.
Ten candidates will take the stage: Mr Trump, Dr Carson and Mr Bush; senators Marco Rubio, Ted Cruz and Rand Paul; former Hewlett-Packard chief executive Carly Fiorina; Arkansas ex-governor Mike Huckabee; and governors John Kasich of Ohio and Chris Christie of New Jersey.
The debate is seen as a prime opportunity for Mr Rubio, whom many consider the most serious establishment challenger beyond Mr Bush to go up against Mr Trump and Dr Carson, neither of whom has held elective office.