Nobody is more nervous about this week's debate than Jeb Bush’s top fundraisers -- and no audience will have more to say about his future viability as a candidate.

New York Jets owner Woody Johnson knew it. He recognized the group assembled at his Rockefeller Center office in Manhattan last Wednesday was in need of some reassurance after Bush’s unimpressive performance in last month’s GOP debate, so Bush’s national finance chairman, recalled one attendee, gave a personal pledge: Jeb would be “well prepared” for the second debate this week.


He’d better be. Five-plus months before the first ballots are cast, Bush faces the kind of do-or-die moment most top-tier candidates confront far later in the primary process – a chance to revive a campaign that has shattered fundraising records, but sunk as low as 6 percent in recent national polls.

Bush, one former adviser to his father said, "needs to show he’s the tough-minded guy we know he is." If he doesn’t, the former aide added, "Well, you know, it might be over."

The Bush campaign privately thinks Bush’s slow-burning fuse – evidenced on the golf course and in sometimes-testy debate sessions – has at long last been lit. But the biggest fear, expressed by Bush allies, donors and party operatives to POLITICO, is that another lousy debate performance will precipitate an exodus of the big money ($100 million-plus in super PAC and campaign cash so far) that has kept the former Florida governor afloat despite his dismal poll numbers.

“The most important thing that Jeb Bush can do right now is to project strength,” says Eric Fehrnstrom, Mitt Romney’s senior adviser in 2012. “Trump's attacks on Bush as a low-energy candidate have taken their toll. For starters, Bush needs to stop referring to him as "Mr. Trump." That sounds like he works for him.”

That attitude is seeping inside the Bush camp as donors watch Donald Trump, and more recently, Ben Carson, zoom past their man. Last month, after Bush left a fundraising dinner at the Hamptons home of retired hedge fund manager Julian Robertson, guests lingered to discuss the necessity of a strong second debate performance. Another lackluster showing, some groused, would make it a lot harder for them to pump their networks for cash, the person told POLITICO.

Bush's problem isn’t merely a matter of being labeled the scion of the loathed GOP political elite, it’s a question of tone. He’s polite, reasonable, bilingual — and the party’s base wants a fighter like Trump who is blustery, visceral and a defiant monolingual speaker of the language his new buddy Sarah Palin calls “American.”

Bush is fond of saying he’s his “own man,” with an emphasis on the “own” part -- to shrug off the gilded albatross of his family’s mixed political legacy -- but these days Trump is making Bush answer for the word “man” too.

Trump has attacked everybody in the field who threatens him but no one as effectively as Bush, insulting Bush’s wife on Twitter, slamming him as “low-energy,” and suggesting over and over that Bush might be too much of a wimp to put up a fight against the Democrats, or anybody else.

“This is a big moment, not unlike the one his brother faced in 2000 when he lost New Hampshire to John McCain,” says veteran consultant Alex Castellanos, who has worked for George H.W. and Jeb Bush. “He has to make an adjustment. He has to sharpen it up. His brother was able to do that in the South Carolina primary, we’ll see if Jeb is able to do that this week.”

How Bush responds to this assault on his character will go a long way in determining whether he is equal to the task posed by a brash developer and reality-TV star with a limitless stock of cash and wisecracks.

The former governor knows the stakes all too well, his people say. And Trump’s challenge has stoked a stubborn competitive streak few outsiders see, according to people close to his campaign.

But reconciling Bush’s courtly diffidence with the grubby demands of the 2016 debate stage won’t be easy. Trump is the most proficient onstage heckler in the business – with an eye for tweaking his patrician foil – but Bush must throw his elbows carefully or risk his reputation as an even-tempered grown-up.

One Bush adviser, hinting at the candidate’s personal feelings about Trump, likened the risks to “getting into the mud with a pig.”

Bush wasn’t terrible at the first debate, held on August 6th in Cleveland, but he played it safe like an incumbent instead of the struggling first-time presidential hopeful he actually is.

Heading into Cleveland, Bush’s team cast Trump as a colorful clown who would hog the spotlight for a few months and then disappear – a benign distraction.

In reality, Bush, according to multiple sources in his camp, was incensed when Trump retweeted a follower’s post that “#JebBush has to like the Mexican Illegals because of his wife" in early July. But he avoided taking a real shot at Trump onstage, denying a POLITICO report that he had privately railed against the developer’s comments – admitting only that “I have said that Mr. Trump’s language is divisive.”

The optics of Bush’s performance weren’t exactly alpha either. After a decade-long absence from the debate stage he appeared a little jittery and unsure of himself, compared to reality-star Trump who looked as comfortable as he did in the boardroom set of “The Apprentice.”

To the surprise of people in his orbit, Bush initially told aides he thought he’d done pretty well -- a judgment eerily reminiscent of Barack Obama’s chipper reaction to his own catastrophic first debate against Mitt Romney in 2012.

But that sunny assessment soon faded, people around him told POLITICO, and he headed to the RedState confab in Georgia a few days later determined to start throwing punches he’d pulled in Cleveland. Bush won over a very conservative audience inclined to be skeptical of his candidacy, in part, by criticizing Trump’s post-debate verbal assault on Fox debate moderator Megyn Kelly.

"Do we want to win?" Bush asked, to applause. "Do we want to insult 53 percent of all voters? What Donald Trump said is wrong. That is not how you win elections. Worse yet, that is not how you bring people together to solve problems.”

None of this has translated into actual popularity with GOP voters, however. In the five weeks since the first debate, he’s ceded his second-place position to Ben Carson, sinking from 10 percent of the national vote to high single-digits.

But several Bush advisers said he’s given up illusions of being a frontrunner, and of emerging from the Republican primary without getting down in “the mud” with Trump. But how far to go? The key, people close to Bush say, is coming up with a tough approach without making the candidate want to crawl out of his own, deeply civil skin. To that end, he has been huddling with his team, whenever time permits, to work out a plan of attack for the primetime showdown with Trump at the Reagan Library Wednesday.

George H. W. Bush had Lee Atwater, a bare-knuckled campaign operative who repelled the charge that his boss was an out-of-touch “wimp” by unleashing the infamous Willie Horton ad on Mike Dukakis; George W. Bush nursed a nice-guy reputation, but unleashed Karl Rove against Al Gore and John Kerry to devastating effect. No “turd blossom” (Bush 43’s nickname for Rove) blooms in Jeb Bush’s political garden, and that makes the tough-guy pivot a little harder, though not impossible.

His top advisors, led by longtime aide Sally Bradshaw, are hardly pushovers -- but they’ve never faced anybody quite like Trump either and they have been more focused on fundraising, organization building and policy formulation than polishing the brash knuckles.

The sessions have been led by Bradshaw, and supplemented with coaching from outsiders, including former Romney adviser Peter Flaherty. Bush, people close to the process say, has urged the participants to challenge him; three staffers have emerged as increasingly influential in these closed-door sessions, POLITICO has learned – campaign manager Danny Diaz, communications director Tim Miller and Trent Wisecup, who have helped hone Bush’s counterattack.

Wisecup, who helped review Bush’s gubernatorial emails for a recently released ebook, has been a particularly important figure in the prep sessions, in part, because he’s urged the boss to be much more aggressive and pelted the candidate with Trump-like lines of attack. A colorful and combative veteran Capitol Hill aide, Wisecup is known for his love of a good fight: his Twitter avatar features a gloves-in-your-face photo of heavyweight champ Joe Louis. Back in 2007 Wisecup gained fleeting YouTube fame for a long tirade against an anti-Iraq war protester he berated for being “un-American.”

Miller, an opposition researcher by trade, has prepped Bush with reams of background on Trump – from his long history of controversial remarks to his past support of Democratic causes.

Miller declined to comment on the preparations but hinted that the Trump-as-a-liberal theme would come up. The former governor, he said, would seek to “distinguish himself from the field and candidates like Trump who has an avowedly liberal track record and wants to massively increase power and resources in Washington D.C.”

What’s also clear, to those who’ve spoken to Bush, is that his dislike of Trump remains intense. During a recent conversation with several friends, the former governor ripped Trump as “poll-tested.” While the real estate mogul has won legions of fans for appearing unvarnished, Bush sees him as rehearsed – and lacking any deeply-held convictions other than his own desire for self-aggrandizement.

Bush has told friends he even thinks Trump actually “scripted” his apparently off-the-cuff insult of John McCain’s war record.

Still, hitting Trump in the press and getting in his face are two very different things, and Bush has always been averse to ugly confrontation.

And they will be literally standing cheek to cheek at the library: During a conference call outlining logistics last week, CNN officials informed campaigns that each podium will be less than two feet from each other. The library’s stage, small to begin with, must accommodate 11 candidates.

Bush has taken to whacking at Trump in his pointed but decorous way – questioning the one-time pro-choice, pro-Clinton, pro-single-payer-health-care over his bona fides as a Republican. One of his favorite jabs: that after Nancy Pelosi became House speaker in 2007, he sent her a congratulatory note calling her “the greatest.”

And his team has gently advised him to avoid his Obama-like tendency to engage in policy lectures or clunky theatrics, like his 1994 challenge to his gubernatorial opponent Lawton Chiles to “look into the eyes” of a businessman Bush believed Chiles had insulted.

A positive example? One longtime member of the Bush inner-circle suggested “the right tone” would be to emulate George W’s what’s-wrong-with-this-guy attitude when Al Gore invaded his personal space during the 2000 debates. Then there's Jeb Bush's own performance in the final debate of his 2002 re-election campiagn, when he went he-man on Democrat Bill McBride -- portraying him as a policy lightweight. When Bush turned to the late Tim Russert, the moderator, and said "You sense my frustration," Mike Murphy, now the head of Bush's super PAC, leaned forward in his chair and began laughing.

Another danger for Bush, GOP insiders say, is that he’ll leave his toughest anti-Trump attacks outside the debate hall, making him look like the A student who shrinks in the presence of the school bully. Some Republicans warned of the ridicule heaped on another nice-guy candidate -- former Minnesota Gov. Tim Pawlenty -- who went after rival Mitt Romney in TV interviews in 2012 but refused to attack Romney when the two squared off on the debate stage.

“Once you’ve gone from being the joyful tortoise, you have to become the snapping turtle,” said Nelson Warfield, a longtime Republican strategist who has prepared a number of candidates for debates.

Pawlenty, who dropped out of the 2012 race before a single ballot was cast, counseled Bush to accept the mantle that had been thrust on him by the media and prove to voters he’s got the toughness to tackle the bully.

"There is clearly running room for someone in the race to directly take on Trump,” Pawlenty told POLITICO in an email. “If done successfully, it could become a political 'David v. Goliath' story...or, in the case of Jeb taking on Trump, 'Goliath v. Goliath'.”

Marc Caputo contributed to this report.