WASHINGTON – Republicans square off in their latest US presidential debate on Thursday, just 18 days before all-important first votes are cast in the nominations race, after a rising party star delivered an extraordinary rebuke to frontrunner Donald Trump.
Seven candidates will take the main stage in South Carolina, with six focused on how to knock the real-estate tycoon off his perch and finally bring the 2016 campaign to a debate about issues rather than obsession over Trump's celebrity bombast.
South Carolina's young, charismatic governor Nikki Haley, considered by some a potential vice presidential pick, essentially cleared the way for Trump's rivals by attacking the rhetoric of the celebrity billionaire.
Her remarks – "During anxious times, it can be tempting to follow the siren call of the angriest voices. We must resist that temptation" – were all the more potent as they came in the official Republican response to President Barack Obama's State of the Union address on Tuesday.
"Some people think that you have to be the loudest voice in the room to make a difference. That is just not true," she said pointedly.
The message marked political shots fired in the civil war roiling the Republican Party, specifically Trump's outsider populism versus his rivals in the conservative establishment.
By picking Haley, the daughter of Indian immigrants, GOP leaders – who reportedly cleared the speech before she addressed the nation – were effectively announcing they had had it with Trump's toxic brand of ethno-nationalism.
But Trump, who has relentlessly proven his savvy in the campaign, sought to deflect the criticism and turn Haley's hammering into a positive.
"As far as I'm concerned, anger is okay. Anger and energy is what this country needs," Trump told CNN in reacting to Haley's remarks.
"I like her, she's a very nice woman, but she's very weak on the subject of illegal immigration."
The main debate kicks off around 9pm local time, while three low-polling White House hopefuls compete in an undercard event three hours earlier.
On the same day, Republicans in the House of Representatives gather in Baltimore, near the capital Washington, for their annual winter retreat.
Much of their closed-door discussion will focus on the congressional agenda during an election year, including how to improve the immigration system and defeat Islamic State extremists.
But no doubt they also will be mapping out the paths to the presidency that various candidates may or may not be able to pursue successfully – and Trump should figure in those discussions.
'Kardashian of politics'
There is an unquestionable paradox in the establishment drilling into the man who for months has led Republican polls by a substantial margin.
Critics warn he is a self-promoter who lacks the temperament or experience to be president.
"He is the Kim Kardashian of politics," former business executive Carly Fiorina, one of the low-polling rivals, told the Des Moines Register newspaper.
"But this isn't a reality show. It's not entertainment. It's deadly serious now."
The celebrity billionaire has ridden a wave of populist anger with Washington, frustration over the nation's lackluster economic recovery, and fear about a growing terrorism threat.
The latest provocation by Iran, the seizure and then release of 10 US Navy sailors, is sure to fuel accusations from debate candidates that Obama's weak foreign policy is leaving the world more dangerous.
Trump set off a global firestorm by calling for a ban on Muslims entering the US, and has pledged to deport millions of undocumented immigrants if elected.
Rivals are scrambling to keep up, or knock Trump off course.
He will be joined on stage on Thursday by conservative Senator Ted Cruz, his nearest competitor; charismatic Senator Marco Rubio; retired neurosurgeon Ben Carson; New Jersey Governor Chris Christie; Florida's ex-governor Jeb Bush; and Ohio Governor John Kasich.
Party leaders have made it clear they are worried about Trump's impact in November, not just on the presidential election but crucial congressional races.
They see Trump as unable to unite conservatives and moderates enough to help Republicans keep control of both chambers of Congress.
The anti-establishment Trump said he was unfazed by the party leadership's shots across his bow, particularly their green light for Haley's speech.
"They have to do what they have to do," he said.
On February 1, residents of Iowa will be the first Americans to cast their votes in the 2016 race for the presidential nominations of the Democratic and Republican parties.