Baltimore, North Charleston, United States - With the first vote of America's 2016 presidential election just over a fortnight away, unease over Donald Trump's frontrunner status looks set to dominate a primetime debate Thursday.
The controversial celebrity could face a torrent of attacks from the six other Republican White House hopefuls who take to the stage in South Carolina.
Trump has long led the polls and his campaign shows no signs of collapsing before Republicans in Iowa cast their ballots to pick the party nominee on February 1.
On the eve of that vote the party establishment, after months of tip-toeing around the frontrunner, appears to be mustering its forces.
Many party leaders now seem to believe the polarizing populist's inflammatory message is more dangerous for their camp than the risk of him launching an independent run.
South Carolina Governor Nikki Haley fired the opening salvo against Trump during her rebuttal to Barack Obama's State of the Union address on Tuesday.
Calling on Republicans to ignore the "angriest voices" in their party, the possible vice presidential candidate trained her sights as much on Trump as the Democratic president.
The political shot resounded in a Republican Party torn by a struggle between a rebellious rank-and-file drawn to Trump's outsider populism and the party's conservative establishment.
By picking Haley, the daughter of Indian immigrants, GOP leaders - who reportedly greenlighted her speech - were effectively announcing they had had it with Trump's toxic brand of ethno-nationalism.
Party leaders gathering Thursday in Baltimore doubled down.
The question is "how do we have a message that's inspiring, that's inclusive, hopeful, optimistic and that unites the country," said House Speaker Paul Ryan.
"We don't want to have another president like this one that divides the country." Trump, who has repeatedly proven his savvy in the campaign, sought to turn Haley's criticism into a positive.
"As far as I'm concerned, anger is OK. 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." But many of Trump's rivals on the debate stage have heeded the call.
Former Florida governor Jeb Bush, who badly needs a boost to stay in the race, on Thursday unleashed a hard-hitting ad savaging Trump for the way he mocked a reporter with disabilities.
"That's why I called him a jerk," Bush says in the spot.
"What kind of person would you want to have in the presidency who does that? At what point do we say, 'Enough of this, let's start solving problems'?" Senator Ted Cruz has ditched a strategy of not attacking Trump and begun questioning the mogul's "New York City values." That could play well in conservative Iowa, where Cruz and Trump are running neck and neck.
But Cruz, who has run as a ultra-patriotic anti-elitist, may also have his hands full repelling damaging allegations that he secretly borrowed money from Wall Street banks, as well as Trump-fueled suggestions that he cannot be president because of his birth in Canada.
The trio will be joined on stage Thursday by Senator Marco Rubio; retired neurosurgeon Ben Carson; New Jersey Governor Chris Christie and Ohio Governor John Kasich.
The main debate, broadcast on Fox Business Network, kicks off around 9:00 pm (0200 GMT Friday), while three low-polling White House hopefuls compete in an undercard event three hours earlier.
Senator Rand Paul, who missed the cut for the main event, is boycotting the undercard debate.
Trump 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 incident with Iran, the seizure and then release of 10 US Navy sailors, is sure to fuel accusations by the Republican candidates that Obama's weak foreign policy is leaving the world more dangerous.