Editor’s Note: Watch the CNN debate at the Ronald Reagan Presidential Library on Wednesday Sept. 16 at 6 and 8 p.m ET, and get the latest news from CNN Politics

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No one has more on the line in Wednesday night’s Republican presidential debate than Jeb Bush.

The former Florida governor with one of the most recognizable names in politics and $100 million in the bank is facing one of the most crucial moments of his political career at the CNN debate held at the Reagan Library.

In the unpredictable GOP race for president, Bush is struggling to regain his footing in the midst of Hurricane Trump. He first tried to ignore the bellicose billionaire before changing course and punching back hard. He has released detailed tax and immigration reform plans to show he is about substance, not style. He has kept a rigorous pace on the campaign trail, squeezing in Monday meetings with tech leaders in Seattle before heading off to Nevada and Michigan post-debate.

CNN Republican presidential debate

The payoff for all that hard work? A steady slide to the middle of the pack that is giving Bush donors the jitters and an opening to rivals like Ben Carson and Ohio Gov. John Kasich to overtake him in key early-voting states.

Here’s a look at some of the hurdles Bush and other GOP presidential contenders face going into debate night.

Bush

The former Florida governor’s initial assets – money, connections and political experience – have made his downward trajectory all the more striking as he wrestles to regain control of the campaign narrative.

“These debates are increasingly life-and-death moments for candidates who started out as the presumptive frontrunners but have fallen to low single digits,” said Republican strategist Steve Schmidt, who listed Bush, Scott Walker and Marco Rubio in that category. “The first step to securing the nomination, is taking control of your destiny, completely within the process. At this point in 1999, George W. Bush had accomplished that. At this moment in time, Donald Trump has accomplished that,” said Schmidt, a former aide to the elder Bush who advised John McCain in 2008.

“None of these candidates have any ability to control their own destiny any longer—their capacity to rise from 3-, 4-, 5-, 6% is fundamentally about Donald Trump losing his grip,” Schmidt said. “No other candidate, with the possible exception of Ben Carson, is within reach to beat Trump. Only Trump can beat Trump.”

Bush is making a noticeable effort to retake control over his campaign narrative. He’s dropped his hands-off approach to Trump in favor of direct confrontation. He’s letting his personality show more often by, for instance, unbuttoning his shirt over the weekend to reveal a shirt with the 1984 campaign logo of Ronald Reagan and his father.

READ: Jeb Bush speaks Spanish in video celebrating Hispanics

And he released a campaign video on Monday in which he speaks Spanish – defying Trump’s calls that Bush only speak English on the campaign trail. The video also includes a rare appearance from Bush’s wife, Columba, who is an immigrant from Mexico.

“I have lived over half my life here,” she says in English in the video. “We all have the same interests, the same feelings.”

Still, the moves aren’t helping Bush much in the polls. A Monmouth University poll released on Monday found that in New Hampshire, Bush has slipped from second place into a tie for fifth with Carly Fiorina at 7%.

Trump

Given his defiance of the normal rules of political gravity, it’s become difficult to predict the kind of error that would stunt Trump’s momentum.

A stray remark that would offend women? He was quoted in his Rolling Stone cover story last week as saying, “Look at that face,” when Fiorina appeared on television. He went head-to-head with Fox News host Megyn Kelly during and after the first debate hosted by Fox News.

Another turn of phrase that would offend Latinos? Trump has stood by comments that some Mexican immigrants are criminals and rapists, proposed ending universal birthright citizenship and advocated building a wall along the Mexican border. Despite all of that, his support has only grown, though he is viewed negatively by a majority of Hispanics.

READ: Miss Alabama: GOP should be ‘absolutely terrified’ of Trump

“I think debates tend to work in his favor because at their core, they’re performances,” said Republican strategist Kevin Madden, a former Romney adviser. “He’s a celebrity who’s been performing for the better part of 35 years now, so none of this is new to him.”

Trump has shown serious vulnerabilities when it comes to factual matters.

He charged conservative radio host Hugh Hewitt with “gotcha” questions when Hewitt tested his knowledge about the leaders of terror groups like Hamas, Hezbollah, al-Nusra and ISIS. He also has mischaracterized elements of the Iran deal and made difficult-to-substantiate claims that Syrian Christians have a harder time entering the U.S. than Syrian Muslims.

“One of the interesting things to watch will be whether or not the moderators or other campaigns seek to expose Trump as a bit of a fraud or a con when it comes to being able to promote a conservative Republican agenda,” Madden said. “If he’s exposed as totally unserious on that (foreign policy and national security) issue, it could help some of the other campaigns begin to really draw a favorable contrast on an issue that will be very important in 2016.”

Walker

Walker’s campaign has been in free-fall over the last several weeks, most notably in Iowa where he was the consistent leader in the polls for much of this spring.

READ: Scott Walker: I will stop ‘big-government union bosses’

But there’s been plenty of bad news for Walker lately in Iowa, which is vital to his campaign’s prospects. Walker held the top spot in the pack in polls early this summer, but in a Quinnipiac University poll released last week, Walker had fallen from first place at 18% in July to 10th place in September at 3%.

In CNN/ORC’s polling, Walker has fallen from 10% support nationally in July to 8% in August and 5% earlier this month. In Monday’s ABC News/Washington Post poll, Walker was at 2% nationally, down from 13% in July.

“Walker needs a debate performance that reverses the trajectory of his campaign,” Madden said. “He started out very fast, but didn’t match the initial interest in his campaign with a lot of enthusiasm and momentum once voters started to tune in a little bit more.”

Fiorina

The debate will offer the first chance for Fiorina to directly square off against Trump.

Another forceful performance could keep her momentum growing, but if she’s overshadowed, it’s hard to see her building more steam to keep overtaking competitors with much higher name recognition.

Fiorina, the former head of Hewlett-Packard, made it to the main stage on the strength of her first debate performance, raising expectations for her on Wednesday night. Charting the opposite trajectory of Walker, Fiorina has climbed steadily in the polls since the first debate – a rise that CNN recognized with an amendment to the debate criteria that secured her spot.

Still, Fiorina has hovered in the single digits, according to CNN/ORC’s polling. In ABC News/Washington Post’s most recent poll, she went from an asterisk in July to 2% this month.

She led the pack in the National Federation of Republican Women’s straw poll conducted over the weekend – notching nearly half of the vote when the first and second choice spots were combined. At that conference, she also garnered attention with an indirect attack on Trump during a well-received speech, where she also directed plenty of attacks against Democratic front-runner Hillary Clinton.

Carson

The understated style of retired neurosurgeon Ben Carson has served him well in recent months, helping build a loyal following among evangelical voters and a professional campaign organization that has turned out big crowds even in deep blue states like California.

But with the exception of a few memorable lines in the first debate, he is widely viewed as having been too quiet – and Trump has attacked his energy level. Carson has also seemed skittish about taking on Trump – at one point questioning the authenticity of his faith but then walking back that criticism and saying he didn’t mean it.

He has said he doesn’t want to get into a “gladiator fight” with Trump, but, at the same time, he must show Wednesday that he has the mettle to take him on.

The risk for Carson and all the candidates, of course, is being aggressive but not crossing a line where their attacks work to Trump’s benefit.

Rubio

Many Republican donors and strategists are still eyeing Rubio as one of the most formidable contenders for the Republican nomination, given his charisma and compelling narrative on the campaign trail. Like the other top-tier candidates, Rubio has faded into the shadow of Trump.

But he was viewed as having a strong debate performance in the first faceoff among the candidates. Given his youth, his challenge is to show that he has the gravitas to serve as the party’s standard bearer.