Republican contender Marco Rubio has struggled at a presidential debate at the worst possible time.
The junior senator from Florida potentially confounded his bid on Sunday to emerge as Donald Trump's chief rival in New Hampshire and gave hope to three rivals desperate for a strong showing.
Under assault from New Jersey Governor Chris Christie over his level of experience as a first-term US senator, Rubio retreated time and again to canned statements from his stump speech and looked uncomfortably rattled.
"Marco, the thing is this," Christie said during one heated exchange, "when you're president, when you're a governor of a state, the memorised 30-second speech where you talk about how great America is at the end of it doesn't solve one problem for one person."
While Rubio recovered later in the debate, the timing of his performance was terrible, coming three days before New Hampshire Republicans register their choices on Tuesday in the nation's second nominating contest.
The debate at St Anselm College was the last face-off of the candidates before the vote.
Rubio's tough moments may breathe new life into the campaigns of Christie, former Florida Governor Jeb Bush and Ohio Governor John Kasich, three experienced politicians who, like Rubio, represent establishment Republicans.
All three have suffered from the dominance of front-runner Trump in the Republican race.
They are badly in need of a breakout moment to change the trajectory of the battle in New Hampshire, where the polls show Trump in the lead, Rubio in second and Texas Senator Ted Cruz in third place.
Trump did not have his best debate. He looked flustered in a fight with Bush over the use of eminent domain in advancing the interests of public use projects and private industry.
But he seemed to do well enough to possibly win on Tuesday in what would represent his first victory of the 2016 race, erasing the pain from a loss in the Iowa caucus last week, where he finished second to Cruz and just ahead of the surging Rubio.
A victory in New Hampshire could put Trump on track for more wins in South Carolina on February 20 and beyond on the way to the November 8 election.
For the second debate in a row, Bush looked polished and sounded like the candidate many establishment Republicans had pinned their hopes on. His problem is it may be too late.
Kasich, likely to end his candidacy if he does not do well on Tuesday, delivered a positive message that could appeal to New Hampshire Republican voters, who famously make up their minds late and never seem in the mood to follow the lead of the Iowa caucuses, won by Cruz.
The trouble for Rubio began soon after the debate started when the ABC News moderators asked Christie about Rubio's experience in the US Senate and Christie pressed his case.
