Republican presidential candidate Donald Trump celebrates victory in the South Carolina primary on February 20, 2016 in Spartanburg, South Carolina
Washington (AFP) - Donald Trump and his flummoxed rivals take the stage for a crucial presidential primary debate, with fellow White House hopefuls wondering what magic words can stop the brash billionaire's march toward the Republican nomination.
The Grand Old Party and its non-Trump contenders for the White House are under intense pressure to derail the Trump train, so the knives may come out in Houston, Texas at the final Republican debate before "Super Tuesday," the delegate-rich, single-day run of about a dozen state primaries on March 1.
The five-man debate, which begins at 7:30 pm (0130 GMT Friday) and will be carried live by CNN, promises to be stormy.
By turns boastful, mocking or menacing, Trump has hit on a style that has seduced a growing and increasingly diverse share of Republican voters -- to the dismay of his rivals, who have struggled to find an effective angle of attack against the 69-year-old real estate mogul.
Senators Marco Rubio of Florida and Ted Cruz of Texas, the only two candidates given any real chance of beating Trump, know that the stakes could not be higher.
Retired neurosurgeon Ben Carson remains in the race but hardly anyone seems to be paying him any attention.
And Ohio Governor John Kasich, who has a more moderate and less gloomy message about the state of America than his rivals, knows he will be under mounting pressure to withdraw from the race so that the "anti-Trump" forces can coalesce around Rubio.
Trump seems unfazed by that possibility.
"It's going to be an amazing two months," he boasted Tuesday in a victory speech in Nevada, confidently predicting sweeping wins that will help him clinch the nomination long before the Republican convention in Cleveland in July.
"We might not even need the two months, to be honest."
Cruz remains defiant, insisting he is the best candidate to topple Trump, and said he expects his home field advantage will help him claim the strategically vital Texas, which he called "the crown jewel" of Super Tuesday.
- Rubio trails in Florida -
Cruz won the first Republican nominating contest, in Iowa.
But after three consecutive Trump victories -- in New Hampshire, South Carolina and Nevada -- and with his frontrunner status confirmed by the polls, some wonder whether Trump will tone down his incendiary rhetoric, and adopt a more "presidential" pose on Thursday night.
Will he attack Rubio with the same ferocity, now that longtime whipping post Jeb Bush has stepped out of the ring?
"Marco Rubio's a nice young man. I can't hit him, he hasn't hit me," Trump said this week.
But, "when he hits me, oh, is he going to be hit."
While Rubio has been holding his punches, Vice President Joe Biden unleashed harsh criticism against Trump Thursday, assailing his "dangerous" rhetoric on immigration.
Vicente Fox, Mexico's president from 2000 to 2006, took a harsher tone, using an expletive in telling the Fusion television network that Mexico was not going to pay for the border wall proposed by Trump.
Fox "horribly used the F word when discussing the wall. He must apologize!" an angry Trump posted on Twitter. "If I did that there would be a uproar!
Hours before the debate, a Quinnipiac University poll sounded what could be a death knell for the hopes of party elders intent on blocking Trump's advance: it showed Trump handily winning in Florida, Rubio's home state.
It found that 44 percent of Republicans there would vote for Trump, compared to 28 percent for Rubio. Cruz would place third with 12 percent, according to the February 21-24 survey of likely Republican primary voters.
"If Rubio can't win in his home state, it is difficult to see how he can win elsewhere," said Peter Brown, the poll's assistant director.
The March 15 Florida primary is among the juiciest prizes of the Republican nomination race because it is the first big battleground where the winning candidate scoops up all of the state's delegates.
Some within the party still expect a long fight and cling to a scenario in which Trump, Rubio and Cruz stay in the race until the convention, with none gaining an absolute majority of delegates.
In this case, after a first round, delegates would be released from their initial commitment and could vote for the candidate of their choice in a second round, thereby reshuffling the electoral deck.