PORTSMOUTH, NH — (CNN) Jeb Bush’s presidential campaign is facing a full-blown existential crisis.

The former Florida governor’s attempt to revive his White House hopes during Wednesday’s Republican debate by taking on his former protege, Sen. Marco Rubio, backfired badly.

Instead, he delivered a performance drained of passion, fire and inspiration followed by a testy post-game interview that added up to a disastrous night for Bush.

Bush was already struggling going into the debate — grappling with low poll numbers and a weak base in early voting states.

But his performance only confirmed and deepened damning perceptions of his political skills and questions about his stomach for the fight. And Bush is already trying to stave off the stench of decay that quickly gathers around losing campaigns.

“The end is not near — life is good,” he told reporters in New Hampshire on Thursday.

But when a candidate is forced to make such a statement, and when the political classes begin to ask questions about how long a campaign can stay in the race, it’s never good news.

“I think his campaign is on life support,” said Ford O’ Connell, a Republican political consultant not currently affiliated with a 2016 presidential candidate.

Former Minnesota Gov. Tim Pawlenty, a Republican who unsuccessfully ran for the White House in 2012, said that Bush had “underperformed” all along, and now needed a quick fix.

“He is going to have to up his game or the market place is going to move away from him,” Pawlenty said on CNN.

David Axelrod, a former Democratic political guru who is now a CNN analyst, said that Bush endured a “terrible night.”

“I think it put him in a really dangerous position,” said Axelrod.

Bush’s trip to New Hampshire was planned to build on hoped-for momentum after the debate in Boulder, Colorado, and to launch the kind of revivalist mojo that John McCain conjured up in the 2008 campaign.

Instead, the trip is being overshadowed by a media post mortem not just of Bush’s debate performance but his entire campaign.

“It is not on life support, we have the most money, we have the greatest organization. We’re going to be fine,” Bush said in Portsmouth, New Hampshire.

Bush also held a meet-and-greet with supporters and appeared alongside a banner reading “Jeb Can Fix It” which was meant to refer to his vow to get Washington working again, but in the light of Wednesday night appeared more like an ironic comment on the need to revive his campaign.

While Bush has the financial muscle, organization and support from a super PAC to stay in the race, sooner of later he must demonstrate genuine lift in his poll numbers, with first nominating votes to be cast in just three months.

The magnitude of Bush’s challenge is rooted in fact that the deficiencies on display Wednesday night, and in evidence throughout his campaign, don’t seem like they might be easily mendable.

They center on the candidate himself and the perceptions of failure now dogging a candidacy clearly suffering from overly high initial expectations. He must worry that donors who powered the fundraising machine at the center of his candidacy will also soon begin to doubt him — or look for a more dynamic candidate elsewhere.

Thursday night, Bush held a conference call with donors, state campaign chairs and other key leaders. Two participants on the call said that Bush acknowledged that he could have done better at the debate, but said he was confident in his campaign’s plan and strategy.

They described the mood as one of concern, not panic. One of the participants noted that many of Jeb’s backers have been through other campaign cycles and aren’t the “run-and-hide types.”

But, the participant said, “that doesn’t mean there aren’t real concerns.”

Then there is the question of how Bush can improve his technique in debates — with the next Republican clash only two weeks away already shaping up as a test in which he will be under an even more unforgiving spotlight.

Speaking in New London, New Hampshire Thursday night, Bush was asked by a reporter what he was going to do to get better in debates.

“Look we’ve got eight more debates,” he said, then added sarcastically, “We’re going to have to do what other candidates do, which is rudely interrupt, not answer the questions that are asked and hopefully the debate moderators will actually ask more substantive questions as well. It’s going fine.”

He was then asked if he was having any fun, to which he responded: “Oh yeah, lots of fun.”

Perhaps the most worrying consideration for Bush is that his performance has opened the door for others — particularly Rubio, who got rave reviews after the debate and now threatens to usurp Bush as the top GOP establishment candidate.

“The establishment buzz around Rubio right now …. is going to help him continue that slow, steady climb into that poll position in the establishment lane,” said Kevin Madden, a former top aide to Mitt Romney who is now a CNN analyst.

The clash between Rubio and Bush may turn out to be one of the most clarifying snapshots of the campaign — because in that moment, the weaknesses of one man were exacerbated by the strengths of another.

In a clearly choreographed attack, Bush seized on complaints that in his desire to wage his presidential campaign, Rubio had neglected his real job and had let Floridians down with his poor voting record in the Senate.

But Rubio unleashed a furious counter-attack, in an almost Shakespearean tableau of a protege spurning his mentor, showing the ruthless guile, killer instinct and willingness to do anything in pursuit of victory that Bush appears to lack.

“The only reason you are doing it now is because we’re running for the same position and someone has convinced you that attacking me is going to help you,” Rubio said.

The riposte was so devastating because it jabbed Bush over the clearly obvious fact that he disdains hardball politics, is desperately trying to find a footing in the campaign and his heart was not really in the attack.

CNN analyst Ana Navarro, who knows both men well, said that the exchange made her teeth hurt. While arguing that Bush remained the best qualified person on the stage to be president, she admitted he needed to pull off a swift recovery.

“He has got to figure out a way how to slay and kill this debate boogie monster dead,” she said.

A key Bush supporter in New Hampshire said on condition of anonymity that he believed that his candidate could still pull off a comeback, and said the debate format did little to help Bush or showcase his mastery of policy or problem solving skills.

“He will do what he has to do on site — when he is visiting New Hampshire and stay connected to the people,” the supporter said.

In a post-debate interview with CNN’s Dana Bash, Bush implicitly admitted that he lacks the histrionics that help candidates prosper on debate stages and appeared frustrated, complaining that the CNBC moderators asked a question about fantasy football and not real issues that mattered.

“Nope, not frustrated,” Bush told Bash, though his thin grin and demeanor appeared to indicate otherwise.

“I’m running for president of the United States. I’m running with heart. I’m not a performer. If they’re looking for an entertainer-in-chief, I’m probably not the guy,” he said.

Bush appears to ignore the fact that performance is fundamental to politics, according to some observers.

“Part of leadership is to inspire and in this media, news, political world, you have to be inspiring,” said Pawlenty.

“He is going to have to up his game because the debate last night and even before, the response was that was not sufficiently inspiring.”

And his statement to Bash that if voters are looking for a reform-oriented conservative with a proven record of results, he is the ideal candidate, pointed to a deeper problem for Bush. Simply put, in a year when outside candidates have captured the Zeitgeist voters simply are not yet buying what he is trying to sell.

Bush rejects that criticism: “They are buying it, right now in New Hampshire. More people are going to buy it as we campaign harder,” Bush said Thursday.

But many observers believe Bush might be a victim of poor timing and that his problems could therefore be insurmountable.

“In a lot of other cycles, Jeb could have run and won, but given the sort of groundswell for political outsiders and the ghosts of his last name, it is just very tough,” said O’Connell.

“No matter what he says, he either comes across as privileged or entitled — he just doesn’t seem to be able to overcome it.”

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