MANCHESTER, N.H. — Everything, it seemed, was breaking Marco Rubio’s way.
Inside the Holiday Inn Express hotel, where Mr. Rubio and his top aides had camped out in a small conference room to prepare for last Saturday’s Republican debate, marathon practice sessions were interrupted, giddily, by word of new endorsements from former rivals and fawning phone calls from donors.
At his campaign headquarters a few miles away, 500 volunteers from across the country had gathered inside an expansive maze of corporate-style offices, requiring so much pizza that stacks of empty boxes nearly touched the ceiling.
Over dinners across town, longtime friends of Mr. Rubio dared to speak of a surprise showing in New Hampshire: not just second or third place, but an outright victory.
What they never imagined was the breakdown that could jeopardize it all: a malfunction of the campaign’s single-biggest asset, its most nimble salesman and, until 8:34 p.m. on Saturday, a nearly flawless executioner of its strategy.
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By ABC NEWS on Publish Date February 6, 2016. Photo by Stephen Crowley/The New York Times. Watch in Times Video »But malfunction Mr. Rubio did, in a disastrous debate performance that sent his popularity plunging and relegated him to fifth place in the primary on Tuesday. It is the kind of moment that campaigns turn on, unexpected and unforgettable. And it changed the Republican race in a rapid and powerful way.
The episode was such a shock that not even Mr. Rubio seemed to understand the gravity of the situation as he left the stage at St. Anselm College just after 10 on Saturday night. His wife and four children rushed to greet him in a private back room, followed by somber-faced aides, who delivered their candid assessment.
It was not, Mr. Rubio conceded to them, his best performance. But only after the senator scrolled through Twitter — flooded with brutal, mocking reviews — did he fully grasp the damage he had done to his campaign.
His aides and supporters, on the other hand, had been hearing it all night. “Shocked” was how one supporter close to the campaign leadership described the reaction. The emails pouring in from donors were incredulous. Why did he not fight harder against Gov. Chris Christie of New Jersey, who had mercilessly mocked him as a memorizer of scripted lines? Why did he keep repeating the same talking points? Why was he sweating so much?
At his campaign headquarters in Washington, some of the younger staff members were so deflated that senior advisers met with them on Sunday morning to reassure them the episode was just a hiccup — the kind that happens all the time in presidential races.
But privately, advisers acknowledged, this was different — and avoidable. Mr. Christie had not just telegraphed the attack, he warned Mr. Rubio backstage on Saturday night as the two men waited for their names to be called by the ABC News moderators. “I understand I am going to have a hard time tonight,” Mr. Rubio playfully told Mr. Christie.
“Yes, you are,” Mr. Christie replied, according to three people to whom he recounted the conversation. Todd Harris, a senior Rubio adviser, called the conversation “completely fabricated.”
A few minutes later, on the debate stage, Mr. Christie fulfilled his threat, instructing the audience to watch for Mr. Rubio’s canned lines and then interrupting them with a searingly memorable quip from which the senator never recovered: “There it is everybody,” Mr. Christie said. “The 25-second memorized speech.”
The Rubio campaign declined to comment on its debate preparations and internal conversations. This account of how his campaign stumbled in New Hampshire is based on interviews with dozens of aides, operatives, supporters and advisers, most of whom were granted anonymity to describe moments and conversations that were intended to be confidential.
In the wake of the debate debacle, they are now grappling with the weaknesses of a strategy constructed almost entirely around the political talents of its candidate. Even his longtime admirers seemed unnerved, and their faith in him shaken.
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“Everybody is nervous. I don’t think there’s any other emotion you can have at this point,” said Jorge Luis Lopez, a lawyer in Miami and Rubio supporter who helps the campaign raise money. “It’s new. It’s very new.”
His solace: No major donors are abandoning Mr. Rubio — not yet, anyway. “Right now, there’s no panic,” Mr. Lopez added.
In the weeks leading to the New Hampshire debate, the Rubio game plan that rival Republicans had called laughable was starting to look smart: a seemingly light travel schedule, no blueprint to win outright any of the first four states, and a low-profile, no-drama ethos that rivals, and even a few allies, mistook for disengagement.
In reality, every decision was grounded in extensive research and planning, be it the campaign’s targeted appeal to suburban families, who voted for Mr. Rubio in droves, or his aversion to attacking Republican rivals, which campaign research showed was off-putting to potential female supporters.
Why not, his aides reasoned, just let Donald J. Trump and Senator Ted Cruz of Texas devour each other and have Mr. Rubio stand for something bigger and saner?
His strategists strove to reveal as little as possible about their plans, even as supporters begged them to dispel the image that they were running a languid campaign. Though other Republicans like Mr. Cruz had released lists of supporters throughout Iowa’s 99 counties months ago, Mr. Rubio and his staff sat on theirs until mid-January, despite having dozens of commitments for months.
But as the Iowa caucuses neared, their approach was starting to work. In one of the final ads the campaign ran before voting began in Iowa, actors were shown watching Mr. Rubio speak and nodding their heads in agreement. One staff member, sitting in a restaurant, noticed something encouraging: nearby patrons nodding along, too, mimicking what they were seeing on screen. At a rally outside Des Moines the Saturday before the caucuses, the senator filled a large hotel ballroom with a larger-than-usual crowd of 1,000.
“This doesn’t look like 15 percent,” quipped Adam Hasner, a former colleague of Mr. Rubio’s from their days in the Florida Legislature, referring to the senator’s mediocre standing in the latest Iowa polls.
What seemed to work most powerfully was putting Mr. Rubio in front of a camera — a format, his aides believed, where his eloquence, life story, youthful appeal and positive message could convert voters into supporters better than any campaign brochure or field worker.
Heading into Saturday night, the campaign’s approach was clear: Mr. Rubio would avoid spats with fellow Republicans and present himself as the candidate best prepared to take on the Democrats in a general election.
That was the idea behind what became the most painful moment of his campaign. In debate preparation sessions, Mr. Rubio had practiced quickly pivoting from skirmishes with Republicans, like Mr. Christie, back to his real target: Mr. Obama and, by implication, Hillary Clinton. And he had made the now infamous point many times before — Mr. Obama wanted to fundamentally change America, by dragging it far to the left, and his success in doing so demonstrated that it was ideology, not experience, that really mattered in a president.
But in the debate, Mr. Rubio’s wording was indirect and confusing, even to his staff. And standing on stage, trading rapid-fire barbs with Mr. Christie, he did not spot the trap that the governor had laid for him by warning the audience of Mr. Rubio’s robotic ways. Every word-for-word repetition of his Obama pivot (“he knows exactly what he’s doing”) sounded like a rattled politician reaching for his security blanket.
The split-screen images on television of Mr. Rubio and Mr. Christie were mirrored by the split-screen reactions of their staff in assigned rooms backstage. Mr. Christie’s aides, snacking on Swedish Fish, cheered. When the governor walked into the room a little after 10 p.m., they broke into applause.
Over the next 24 hours, as Mr. Christie gloated in television interviews and on the stump, Mr. Rubio angrily groused to advisers about news coverage saying he had lost his momentum.
Mr. Rubio’s aura of unflappability was pierced, and his opponents pounced — and, to their surprise, he kept looking off-balance. On Monday morning, Mr. Rubio was unusually listless and humorless during a town-hall-style meeting. He paused to reflect on the last 24 hours and the fight he saw ahead — “a very messy and competitive process,” he said.
He was right. A few hours later, at a different event, he inadvertently repeated a line from his stump speech, in an unfortunate echo of his debate mishap. By Primary Day, he was followed from event to event by hecklers who dressed as robots to lampoon his mechanical debate performance.
A few hours later, what was supposed to be a night of triumph turned into a doleful evening of defeat.
Before a dejected crowd that filled just two-thirds of a hotel ballroom here, Mr. Rubio had decided to acknowledge what had become an agonizing reality to everyone around him.
It was all his fault.
“It is on me,” he said, hushing the audience and rejecting their shouted objections. “I did not do well on Saturday.”
“That will never happen again.”