Can any of Donald Trump's rivals find the magic words to stop his triumphal march toward the Republican presidential nomination?
The Grand Old Party's White House contenders face that question as never before as they gather in Houston Thursday for their last debate before "Super Tuesday," the delegate-rich, single-day run of a dozen state primaries on March 1.
The five-way debate, which begins at 7:30 pm local time (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 billionaire.
Senators Marco Rubio of Florida and Ted Cruz of Texas, the only two candidates given any chance of beating Trump, know that the stakes on this Texas evening could not be higher.
Retired neurosurgeon Ben Carson is still in the race but hardly anyone seems to be paying him attention.
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 in a victory speech in Nevada Tuesday, confidently predicting sweeping wins that will clinch the nomination long before the Republican convention in Cleveland in July.
"We might not even need the two months, to be honest."
After three consecutive 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.
Will he attack Rubio with the same ferocity, now that longtime whipping post Jeb Bush has stepped out 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."
Several 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 in the state would vote for Trump, and only 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 Florida primary, which will be held March 15, is the juiciest prize of the Republican nomination race because the winning candidate scoops up all its 99 delegates.
Within the Republican party, some still expect a long fight and cling to a scenario in which three candidates -- Trump, Rubio and Cruz -- stay in the race until the convention, with none gaining an absolute majority of delegates -- 1,237 out of a total 2,472.
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.