PORTSMOUTH, New Hampshire — Jeb Bush emerged from the third Republican debate as a candidate in crisis, with supporters struggling to understand why he keeps underperforming and advisers promising a turnaround before it’s too late.

Campaigning in New Hampshire on Oct. 29, Bush insisted his White House bid was “not on life support.”

Still, advisers concede November will be his campaign’s most crucial period to date, a stark contrast to their previous assertions that Bush was best-positioned to outlast rivals in a long campaign.

Millions of dollars in TV advertising must start yielding stronger poll numbers, advisers say, and Bush himself must find a way to stop being overshadowed by competitors in the large Republican field.

“The intensity is going to increase,” declared Sally Bradshaw, Bush’s Senior Adviser.

To some supporters, that may ring hollow on the heels of Bush’s lackluster performance in Wednesday night’s debate. Aides have spent weeks promising more forceful performances from the bookish former Florida Governor, only to see him repeatedly fall flat.

The former Florida Governor was once seen as the top Republican contender. But he entered the debate in the midst of the most difficult stretch of his White House campaign.

Billionaire Donald Trump dominated in the polls for months, then Ben Carson took the momentum and overtook Trump in polls in Iowa, where the first of the state-by-state contests will be held. Bush has trailed far behind.

The contrast between expectations and reality was particularly striking on the debate stage in Colorado. Bush appeared to land a sharp jab on friend and political mentee Marco Rubio, suggesting the senator should resign if he’s going to keep skipping votes on Capitol Hill while he campaigns for President.

But Bush was glaringly ill-prepared for Rubio’s sharp comeback and quickly faded into the background for the rest of the two-hour contest.

It was a painful moment for Bush and it deepened concerns about a campaign that less than a week ago was forced to drastically cut its payroll, travel costs and other expenses amid slower-than-expected fundraising.

“He was poorly served by whatever campaign adviser told him to go down that path with Marco,” said Brian Ballard, a major fundraiser for both Bush’s campaign and super political action committee. “It’s not the kind of ideas campaign that he has promised.”

Ballard said he still believes Bush would be the most capable commander in chief of anyone in the race, but he acknowledged he is “really worried” about the campaign trajectory.

Bush’s finance team was fielding so many calls from worried donors in the hours after the debate that a special briefing was hastily scheduled Oct. 29.

After Bush made small talk about his trip to New Hampshire, Bradshaw began by addressing the debate head-on, telling donors, “It was not our best night.”

As part of the campaign’s fall revamp, Bush is moving staff out of his Miami headquarters and into early voting states, particularly New Hampshire.

The shift ramps up pressure for him in the first-in-the-nation primary, making it essentially a make-or-break state for his campaign.

Aides say Bush will spend longer stretches of time there, including a bus tour next week. While he still plans to hold town hall-style meetings, he’ll also add more informal events to his schedule, such as stops at VFW halls for beer and lengthy discussions with veterans.

Bush also plans to release a book that chronicles his time as Florida Governor through email correspondence with constituents, another move aimed at helping personalize the son of one President and brother of another.

Supporters in New Hampshire welcome the promise of more campaign resources in their state, but they aren’t ready to declare the new strategy the answer to the candidate’s problems.

“People are sitting on it and watching to see how it evolves,” said Carlos Gonzalez, a New Hampshire state representative and Bush backer.

Another key to Bush’s turnaround strategy, according to aides, is getting a return on his team’s early investment in television advertising.

Right to Rise USA, the main outside group backing Bush, has spent $14.7 million on ads in New Hampshire, Iowa and South Carolina, and has reserved an additional $30 million in television time through the first week of February.

Advisers say the biographical TV spots have improved Bush’s image, especially in New Hampshire, where the campaign’s internal polls show more than half of voters now have a favorable impression of him.

At some point, his super PAC is expected to air advertising critical of other Republicans in the race, especially Rubio, who is seen as the top challenger for Bush’s share of the Republican establishment. However, officials with the group would not say when such ads might begin to air.

Campaign and super PAC officials insisted on anonymity because they were not authorized to publicly discuss the internal planning.

As he travels through New Hampshire and other early states, aides say, Bush will argue that his record in Florida, including cutting taxes, balancing the budget and managing the state through eight hurricanes, best prepares him for the demanding job of President.

In a campaign season where voters are voicing frustration with Washington, he’ll be cast as a problem solver who can get the nation’s capital on track.

As part of that message, Bush’s campaign tested a new slogan at the event in New Hampshire Oct. 29: “Jeb Can Fix It.” Anxious Bush supporters can only hope that’s the case.

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By Julie Pace, Thomas Beaumont and Kathleen Ronayne. AP writer Julie Bykowicz contributed from Washington