Marco Rubio's robotic debate performance on Sunday sparked an all-out offensive on the campaign trail yesterday over his authenticity and experience, momentarily halting the momentum of the senator from Florida and further muddling the presidential nomination battle.

Just before Wednesday's New Hampshire primary, Rubio drew mockery for repeating a rehearsed line four times during the Republican candidates' debate, even after New Jersey Governor Chris Christie had ridiculed him for being a talking-point machine.

Rubio received scathing reviews on the talk shows and was needled by some of his opponents. On Twitter, he earned the moniker "Rubio bot". Clips of the debate played repeatedly on cable news and were watched hundreds of thousands of times on YouTube.

The episode interrupted Rubio's week-long effort to build on his impressive third-place showing in the Iowa caucuses and consolidate donors and party officials behind him. It also appeared to give new life to the struggling candidacies of Christie, former Florida Governor Jeb Bush and Ohio Governor John Kasich, while improving Donald Trump's chances of winning New Hampshire.

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The fallout for Rubio over the long term could be severe. His opponents argued that the debate undercut the central case for Rubio's candidacy - that his political agility and youthful, charismatic persona make him best positioned to challenge the Democratic nominee.

And they claimed a renewed - and seemingly justifiable - rationale to soldier on past New Hampshire, which would mean that the mainstream Republican vote would likely continue to splinter among several candidates.

"The whole race changed last night," Christie said on CNN. "There was a march amongst some in the chattering class to anoint Senator Rubio. I think after last night, that's over. I think there could be four or five tickets now out of New Hampshire because the race is so unsettled now."

Bush also sounded reinvigorated by the troubles of the otherwise polished Rubio, his one-time Florida protege who has overshadowed him all year. "I envy the people that have, you know, message discipline, to say the same thing over and over again," Bush told a standing-room-only crowd in Salem. "Sometimes it doesn't work out."

Kasich, buoyed by a solid debate performance, refused opportunities to go after his opponents and instead asked New Hampshire voters to affirm tomorrow his "unifying positive message". Rubio, for his part, came out swinging in a series of events. He was defiant as he defended his debate-night talking point that portrayed President Barack Obama as a wily operator who has succeeded in enacting a liberal agenda.

"I'm going to say it again," Rubio told a gathering in Londonderry. "The reason why these things are in trouble is because Barack Obama is the first president, at least in my lifetime, that wants to change the country." Nonetheless, the debate haunted Rubio. In the parking lot at his campaign stop in Hudson, someone placed photocopies of the Boston Herald's front page - which showed a picture of Rubio with the headline "Choke!" - under the windshield wipers of cars.

Trump has held a dominant lead in the polls in New Hampshire for months. There was a growing sense on the ground in recent days that Rubio might surf a wave of buzz and goodwill to contend for the top spot, but party strategists said the debate probably closed whatever opening may have existed.

"It's unbelievably volatile," said Steve Duprey, an unaffiliated Republican National Committee member from New Hampshire. "This is the most hotly contested race I've seen since the 1976 Ford-Reagan primary."

The final days in New Hampshire have signalled an unmistakable evolution in the Republican race: For the first time since the summer, it is not revolving solely around Trump.

The campaign has matured, with the non-Trump candidates building their own coalitions, driving their own messages, drawing differences with one another and making their own headlines.