Manchester (United States) (AFP) - Surging Republican hopeful Marco Rubio wilted under sustained attack in the latest US presidential debate, denting his stature going into Tuesday's New Hampshire primary dominated by frontrunner Donald Trump.
The telegenic, 44-year-old Florida senator -- who polls suggest has the best change of winning the White House for the Republicans -- was savaged by his rivals late Saturday for his lack of experience, floundering on a debate stage where he often shines.
A strong showing in New Hampshire would confirm Rubio as the establishment candidate-of-choice for the nomination after his strong third-place finish in Iowa, behind Trump and evangelical US senator Ted Cruz.
Chris Christie, Jeb Bush and John Kasich, meanwhile, need to wrest some of the momentum away from Rubio if they are to keep their presidential dreams alive as the voting schedule shifts south and west.
The most sustained attack was waged by New Jersey governor Christie, a no-nonsense former federal prosecutor who has campaigned hard in New Hampshire and denigrated Rubio for being controlled by his team.
"Marco, the thing is this. When you're president of the United States... the memorized 30-second speech where you talk about how great America is at the end of it doesn't solve one problem," Christie said.
The senator was mocked for repeating the same rehearsed line over and over again -- doing exactly what Christie criticized him for.
"Let's dispel with this fiction that Barack Obama doesn't know what he's doing. He knows exactly what he's doing," Rubio said on a loop.
"There it is: The memorized 25-second speech," Christie interjected.
- 'Leadership' -
The usually-poised Rubio was booed for accusing the governor of dragging his feet in leaving the campaign trail when his state was hit by a deadly East Coast snowstorm last month.
"They had to shame you into going back. You stayed there for 36 hours and then he left and came back," Rubio said.
Meanwhile former Florida governor Bush -- whose dream of following his father and brother into the White House will likely live or die after Tuesday's primary -- stepped up his game, questioning Rubio's experience and butting heads with Trump.
"Leadership. You learn this, you learn it by doing it," he declared "It's not something that you just go up, and on the job do it."
In New Hampshire, Trump commands 35 percent of support among likely Republican voters, a 21-point lead over closest rival Rubio, according to the latest 7News/University of Massachusetts Lowell poll.
Texas Senator Cruz, who won the Iowa caucus but is expected to do less well in New Hampshire, had 13 percent voter support. With nine percent undecided, there is everything to play for.
Even if Trump wins, the party establishment, appalled by his insults, incendiary rhetoric and lack of political experience, is expected to rally behind his potential runner-up.
Bush, whose mother has fondly chastised him for being too polite, laid into Trump for allegedly trying to take the property of an elderly woman in Atlantic City. "That is downright wrong," said Bush.
"Jeb wants to be a tough guy tonight," shot back Trump, whose message of being a winner will take a significant knock if he finishes anything other than first after coming second in Iowa.
"Let me talk. Quiet," added Trump to boos.
Kasich, a Republican governor from the swing state of Ohio, who is on the lookout to tap New Hampshire's independent voters, also made a spirited pitch.
"If I get elected president, head out tomorrow and buy a seat belt, because there's going to be so much happening in the first 100 days, it's going to make your head spin," he told the audience.
The debate got off to a chaotic start when retired neurosurgeon Ben Carson, flagging in the polls, was filmed waiting in the wings as the announcers called him to the stage in vain.
"The acoustics back stage were horrible and there was too much noise out front so you just couldn't hear," he told AFP. "I kept listening for my name, I didn't hear it."
- Trump claims debate victory -
Trump, who boycotted the previous debate, told reporters backstage that he had won the debate, even if a Quinnipiac University poll says 30 percent of the party would not support him.
"I actually think I have the best temperament," he said on stage, when asked about criticism from Cruz that is too hot-headed.
The real estate tycoon has whipped up a passionate following among white blue collar Americans fed-up with career politicians and increasingly frustrated by struggling to make ends meet.
"We have galvanized and created a movement," he added when asked how he would counter Democrat frontrunner Hillary Clinton's quest to make history by becoming the first woman president of the United States.