(CNN) 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.

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.

Photos: Jeb Bush's life Photos: Jeb Bush's life Former Florida Gov. Jeb Bush waves as he takes the stage as he formally announces he is joining the race for president with a speech June 15, 2015, at Miami Dade College in Miami. Hide Caption 1 of 21 Photos: Jeb Bush's life Former Florida governor Jeb Bush shakes hands with attendees after speaking at the 42nd annual Conservative Political Action Conference on February 27 in National Harbor, Maryland. Hide Caption 2 of 21 Photos: Jeb Bush's life Bush takes a selfie with a guest at a luncheon hosted by the Chicago Council on Global Affairs on February 18 in Chicago. Bush delivered his first major foreign policy speech at the event. Hide Caption 3 of 21 Photos: Jeb Bush's life Bush hands out items for Holiday Food Baskets to those in need outside the Little Havana offices of CAMACOL, the Latin American Chamber of Commerce on December 17 in Miami. Hide Caption 4 of 21 Photos: Jeb Bush's life Bush waves to the audience at the Tampa Bay Times Forum in Tampa, Florida, on August 30, 2012, on the final day of the Republican National Convention. Hide Caption 5 of 21 Photos: Jeb Bush's life Bush (left) and wife Columba Bush attend the 2012 Lincoln Center Institute Gala at Frederick P. Rose Hall, Jazz at Lincoln Center on March 7, 2012, in New York City. Hide Caption 6 of 21 Photos: Jeb Bush's life President Barack Obama (left) speaks about Bush (center) while visiting Miami Central Senior High School on March 4, 2011 in Miami, Florida. The visit focused on education. Hide Caption 7 of 21 Photos: Jeb Bush's life Bush (left) speaks with Brazilian President in charge Jose Alancar during a meeting at Planalto Palace in Brasilia, April 17, 2007. Bush was in Brazil to speak about sugar and ethanol business. Hide Caption 8 of 21 Photos: Jeb Bush's life Then-Texas Governor Rick Perry (center) testifies as Bush (right) and then-Arizona Governor Janet Napolitano (left) listen during a hearing before the House Committee on Homeland Security on Capitol Hill October 19, 2005. Hide Caption 9 of 21 Photos: Jeb Bush's life Bush gives a thumbs up signal from his car as he leaves a local polling station after casting his vote in Coral Gables, Florida, November 5, 2002. Hide Caption 10 of 21 Photos: Jeb Bush's life Bush walks out of the West Wing after meeting with his brother, then-President George W. Bush, at the White House January 9, 2002. Governor Bush participated in the signing ceremony of the Everglades Protection Agreement. Hide Caption 11 of 21 Photos: Jeb Bush's life Then-Mexican President Vincente Fox (left) and Bush hold a press conference September 7, 2001, in Miami. Fox visited Florida to attend the Americas Conference and deliver a speech to speak about issues such as immigration. Hide Caption 12 of 21 Photos: Jeb Bush's life Then-President George W. Bush (right) is greeted by Jeb Bush on March 21, 2001, at Orlando International Airport in Orlando, Florida. President Bush was in Orlando to attend the American College of Cardiology Annual Convention. Hide Caption 13 of 21 Photos: Jeb Bush's life Bush speaks during a press conference at the Carandolet Government Palace in Quito, January 18, 2006. Bush and a businessmen delegation were in a two-day visit to talk about a free trade agreement. Hide Caption 14 of 21 Photos: Jeb Bush's life Bush speaks to reporters after meeting with the Florida State Cabinet at the Florida State Capitol Building November 16, 2000, in Tallahassee, Florida. Hide Caption 15 of 21 Photos: Jeb Bush's life Then-President George W. Bush (left) and Jeb Bush (right), raise their arms onstage following a rally at the Florida State Fairgrounds, October 25, 2000, in Brandon, Florida. Hide Caption 16 of 21 Photos: Jeb Bush's life Jeb Bush (left) and then-President George W. Bush stand with their arms around each other's shoulders at a rally in Miami, Florida, September 22, 2000. Hide Caption 17 of 21 Photos: Jeb Bush's life Then-President George W. Bush (right) and Jeb Bush go through the line for strawberries during a stop at the Stawberry Festival March 12, 2000 in Plant City, Florida. Hide Caption 18 of 21 Photos: Jeb Bush's life The Bush family, (left to right) former U.S. President George W., former Florida Governor Jeb, former President George H.W. and his wife Barbara, watch play during the Foursomes matches September 25, 1999 at The Country Club in Brookline, Massachusetts the site of the 33rd Ryder Cup Matches. Hide Caption 19 of 21 Photos: Jeb Bush's life Former President George H.W. Bush (second left), his wife Barbara Bush (left), their son Jeb Bush (center), then-first lady Hillary Clinton (second right), and former then-President Bill Clinton (right) look up to see the U.S. Army Golden Knights parachute team November 6, 1997 at the conclusion of the dedication ceremony of the George Bush Library in College Station, Texas. Hide Caption 20 of 21 Photos: Jeb Bush's life Portrait of the Bush family in front of their Kennebunkport, Maine house August 24, 1986. Pictured, back row: Margaret holding daughter Marshall, Marvin Bush, Bill LeBlond. Pictured, front row: Neil Bush holding son Pierce, Sharon, George W. Bush holding daughter Barbara, Laura Bush holding daughter Jenna, Barbara Bush, George Bush, Sam LeBlond, Doro Bush Lebond, George P. (Jeb's son), Jeb Bush holding son Jebby, Columba Bush and Noelle Bush. Hide Caption 21 of 21

"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.

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.

Photos: Donald Trump's rise Photos: Donald Trump's rise President-elect Donald Trump has been in the spotlight for years. From developing real estate and producing and starring in TV shows, he became a celebrity long before winning the White House. Hide Caption 1 of 37 Photos: Donald Trump's rise Trump at age 4. He was born in 1946 to Fred and Mary Trump in New York City. His father was a real estate developer. Hide Caption 2 of 37 Photos: Donald Trump's rise Trump, left, in a family photo. He was the second-youngest of five children. Hide Caption 3 of 37 Photos: Donald Trump's rise Trump, center, stands at attention during his senior year at the New York Military Academy in 1964. Hide Caption 4 of 37 Photos: Donald Trump's rise Trump, center, wears a baseball uniform at the New York Military Academy in 1964. After he graduated from the boarding school, he went to college. He started at Fordham University before transferring and later graduating from the Wharton School, the University of Pennsylvania's business school. Hide Caption 5 of 37 Photos: Donald Trump's rise Trump stands with Alfred Eisenpreis, New York's economic development administrator, in 1976 while they look at a sketch of a new 1,400-room renovation project of the Commodore Hotel. After graduating college in 1968, Trump worked with his father on developments in Queens and Brooklyn before purchasing or building multiple properties in New York and Atlantic City, New Jersey. Those properties included Trump Tower in New York and Trump Plaza and multiple casinos in Atlantic City. Hide Caption 6 of 37 Photos: Donald Trump's rise Trump attends an event to mark the start of construction of the New York Convention Center in 1979. Hide Caption 7 of 37 Photos: Donald Trump's rise Trump wears a hard hat at the Trump Tower construction site in New York in 1980. Hide Caption 8 of 37 Photos: Donald Trump's rise Trump was married to Ivana Zelnicek Trump from 1977 to 1990, when they divorced. They had three children together: Donald Jr., Ivanka and Eric. Hide Caption 9 of 37 Photos: Donald Trump's rise The Trump family, circa 1986. Hide Caption 10 of 37 Photos: Donald Trump's rise Trump uses his personal helicopter to get around New York in 1987. Hide Caption 11 of 37 Photos: Donald Trump's rise Trump stands in the atrium of the Trump Tower. Hide Caption 12 of 37 Photos: Donald Trump's rise Trump attends the opening of his new Atlantic City casino, the Taj Mahal, in 1989. Hide Caption 13 of 37 Photos: Donald Trump's rise Trump signs his second book, "Trump: Surviving at the Top," in 1990. Trump has published at least 16 other books, including "The Art of the Deal" and "The America We Deserve." Hide Caption 14 of 37 Photos: Donald Trump's rise Trump and singer Michael Jackson pose for a photo before traveling to visit Ryan White, a young child with AIDS, in 1990. Hide Caption 15 of 37 Photos: Donald Trump's rise Trump dips his second wife, Marla Maples, after the couple married in a private ceremony in New York in December 1993. The couple divorced in 1999 and had one daughter together, Tiffany. Hide Caption 16 of 37 Photos: Donald Trump's rise Trump putts a golf ball in his New York office in 1998. Hide Caption 17 of 37 Photos: Donald Trump's rise An advertisement for the television show "The Apprentice" hangs at Trump Tower in 2004. The show launched in January of that year. In January 2008, the show returned as "Celebrity Apprentice." Hide Caption 18 of 37 Photos: Donald Trump's rise A 12-inch talking Trump doll is on display at a toy store in New York in September 2004. Hide Caption 19 of 37 Photos: Donald Trump's rise Trump attends a news conference in 2005 that announced the establishment of Trump University. From 2005 until it closed in 2010, Trump University had about 10,000 people sign up for a program that promised success in real estate. Three separate lawsuits -- two class-action suits filed in California and one filed by New York's attorney general -- argued that the program was mired in fraud and deception. Trump's camp rejected the suits' claims as "baseless." And Trump has charged that the New York case against him is politically motivated. Hide Caption 20 of 37 Photos: Donald Trump's rise Trump attends the U.S. Open tennis tournament with his third wife, Melania Knauss-Trump, and their son, Barron, in 2006. Trump and Knauss married in 2005. Hide Caption 21 of 37 Photos: Donald Trump's rise Trump wrestles with "Stone Cold" Steve Austin at WrestleMania in 2007. Trump has close ties with the WWE and its CEO, Vince McMahon. Hide Caption 22 of 37 Photos: Donald Trump's rise For "The Apprentice," Trump was honored with a star on the Hollywood Walk of Fame in January 2007. Hide Caption 23 of 37 Photos: Donald Trump's rise Trump appears on the set of "The Celebrity Apprentice" with two of his children -- Donald Jr. and Ivanka -- in 2009. Hide Caption 24 of 37 Photos: Donald Trump's rise Trump poses with Miss Universe contestants in 2011. Trump had been executive producer of the Miss Universe, Miss USA and Miss Teen USA pageants since 1996. Hide Caption 25 of 37 Photos: Donald Trump's rise In 2012, Trump announces his endorsement of Republican presidential candidate Mitt Romney. Hide Caption 26 of 37 Photos: Donald Trump's rise Trump speaks in Sarasota, Florida, after accepting the Statesman of the Year Award at the Sarasota GOP dinner in August 2012. It was shortly before the Republican National Convention in nearby Tampa. Hide Caption 27 of 37 Photos: Donald Trump's rise Trump appears on stage with singer Nick Jonas and television personality Giuliana Rancic during the 2013 Miss USA pageant. Hide Caption 28 of 37 Photos: Donald Trump's rise In June 2015, during a speech from Trump Tower, Trump announced that he was running for President. He said he would give up "The Apprentice" to run. Hide Caption 29 of 37 Photos: Donald Trump's rise Trump -- flanked by U.S. Sens. Marco Rubio, left, and Ted Cruz -- speaks during a CNN debate in Miami on March 10. Trump dominated the GOP primaries and emerged as the presumptive nominee in May. Hide Caption 30 of 37 Photos: Donald Trump's rise The Trump family poses for a photo in New York in April. Hide Caption 31 of 37 Photos: Donald Trump's rise Trump speaks during a campaign event in Evansville, Indiana, on April 28. After Trump won the Indiana primary, his last two competitors dropped out of the GOP race. Hide Caption 32 of 37 Photos: Donald Trump's rise Trump delivers a speech at the Republican National Convention in July, accepting the party's nomination for President. "I have had a truly great life in business," he said. "But now, my sole and exclusive mission is to go to work for our country -- to go to work for you. It's time to deliver a victory for the American people." Hide Caption 33 of 37 Photos: Donald Trump's rise Trump faces Democratic nominee Hillary Clinton in the first presidential debate, which took place in Hempstead, New York, in September. Hide Caption 34 of 37 Photos: Donald Trump's rise Trump apologizes in a video, posted to his Twitter account in October, for vulgar and sexually aggressive remarks he made a decade ago regarding women. "I said it, I was wrong and I apologize," Trump said, referring to lewd comments he made during a previously unaired taping of "Access Hollywood." Multiple Republican leaders rescinded their endorsements of Trump after the footage was released. Hide Caption 35 of 37 Photos: Donald Trump's rise Trump walks on stage with his family after he was declared the election winner on November 9. "Ours was not a campaign, but rather, an incredible and great movement," he told his supporters in New York. Hide Caption 36 of 37 Photos: Donald Trump's rise Trump is joined by his family as he is sworn in as President on January 20. Hide Caption 37 of 37

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.

"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.

Photos: Scott Walker's career Photos: Scott Walker's career Wisconsin Gov. Scott Walker dropped out of the presidential race on Monday, September 21. He was seeking the Republican Party's nomination. Hide Caption 1 of 22 Photos: Scott Walker's career Walker fields questions from Bruce Rastetter at the Iowa Agriculture Summit on March 7, 2015 in Des Moines, Iowa. Hide Caption 2 of 22 Photos: Scott Walker's career Walker speaks at the annual Conservative Political Action Conference at National Harbor, Maryland, outside Washington, D.C. on February 26, 2015. Hide Caption 3 of 22 Photos: Scott Walker's career Walker speaks to guests at the Iowa Freedom Summit on January 24, 2015, in Des Moines, Iowa. Hide Caption 4 of 22 Photos: Scott Walker's career Walker speaks at his election night party November 4, 2014, in West Allis, Wisconsin. Walker defeated the Democratic challenger Mary Burke. Hide Caption 5 of 22 Photos: Scott Walker's career Walker shakes hands with Democrat challenger Mary Burke before facing off in a debate at the WMVS-TV studios October, 17, 2014, in Milwaukee, Wisconsin. Hide Caption 6 of 22 Photos: Scott Walker's career Walker has a scarf put on his head during a special service at the Sikh Religious Society of Wisconsin for the victims of the shooting at the Sikh Temple of Wisconsin the previous day, on August 6, 2012, in Brookfield, Wisconsin. Hide Caption 7 of 22 Photos: Scott Walker's career Walker speaks during the Republican Jewish Coalition spring leadership meeting at The Venetian Las Vegas on March 29, 2014. Hide Caption 8 of 22 Photos: Scott Walker's career Scott Walker (left) shakes hands with Chinese President Xi Jinping (center) before a meeting as Iowa Governor Terry Branstad (right) looks on at the Great Hall of the People in Beijing on April 15, 2013. Hide Caption 9 of 22 Photos: Scott Walker's career Walker poses with a woman during the Republican National Convention at the Tampa Bay Times Forum on August 28, 2012, in Tampa, Florida. Hide Caption 10 of 22 Photos: Scott Walker's career Walker prepares to cast his ballot at Jefferson School to vote in the gubernatorial recall election June 5, 2012, in Wauwatosa, Wisconsin. Hide Caption 11 of 22 Photos: Scott Walker's career Walker (right) listens to Louisiana Gov. Bobby Jindal speak as they campaign at the Waukesha Victory Center on May 24, 2012, in Waukesha, Wisconsin. Hide Caption 12 of 22 Photos: Scott Walker's career Walker addresses the National Rifle Association Leadership Forum April 13, 2012, in St. Louis, Missouri. Hide Caption 13 of 22 Photos: Scott Walker's career Walker stands on the North Lawn of the White House before making remarks to the news media after a meeting of the National Governors Association with President Barack Obama on February 27, 2012. Hide Caption 14 of 22 Photos: Scott Walker's career President Barack Obama receives a Milwaukee Brewers baseball jersey from Walker (left) as he disembarks from Air Force One upon arrival at General Mitchell International Airport in Milwaukee, Wisconsin, February 15, 2012. Hide Caption 15 of 22 Photos: Scott Walker's career Walker listens during the 2011 Governors Summit of U.S. Chamber of Commerce June 20, 2011, in Washington, D.C. Hide Caption 16 of 22 Photos: Scott Walker's career Members of Code Pink (left to right) Medea Benjamin, Liz Hourican and Tighe Barry, hold signs to protest as Walker (center) takes his seat during a hearing before the House Oversight and Government Reform Committee April 14, 2011, on Capitol Hill in Washington, D.C. Hide Caption 17 of 22 Photos: Scott Walker's career Walker holds a letter from democratic State Sen. Mark Miller, one of the fourteen Wisconsin state senators who fled the state over two weeks ago, during a press conference on March 7, 2011, in Madison, Wisconsin. Hide Caption 18 of 22 Photos: Scott Walker's career Walker holds up a 'Wisconsin is open for business' bumper sticker as he speaks during a ceremonial bill signing outside his office at the Wisconsin State Capitol on March 11, 2011, in Madison, Wisconsin. Hide Caption 19 of 22 Photos: Scott Walker's career Walker delivers his budget address to a joint session of the legislature at the capitol March 1, 2011 in Madison, Wisconsin. Hide Caption 20 of 22 Photos: Scott Walker's career Walker speaks at a news conference inside the Wisconsin State Capitol February 21, 2011, in Madison, Wisconsin. Hide Caption 21 of 22 Photos: Scott Walker's career President Obama receives a Green Bay Packers NFL football team jersey with 'Obama #1' written on it from Walker (left) at Austin Straubel International Airport in Green Bay, Wisconsin, on January 26, 2011. Hide Caption 22 of 22

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.

Photos: Carly Fiorina's political career Photos: Carly Fiorina's political career Former business executive Carly Fiorina speaks to guests gathered at the Point of Grace Church for the Iowa Faith and Freedom Coalition 2015 Spring Kickoff on April 25, 2015, in Waukee, Iowa. Hide Caption 1 of 15 Photos: Carly Fiorina's political career Fiorina prepares to speak to guests gathered at the Point of Grace Church for the Iowa Faith and Freedom Coalition 2015 Spring Kickoff on April 25, 2015, in Waukee, Iowa. Hide Caption 2 of 15 Photos: Carly Fiorina's political career Fiorina speaks to guests gathered at the Point of Grace Church for the Iowa Faith and Freedom Coalition 2015 Spring Kickoff on April 25, 2015, in Waukee, Iowa. Hide Caption 3 of 15 Photos: Carly Fiorina's political career Fiorina greets guests at the Johnson County Republicans Spaghetti Dinner at Clear Creek Amana High School on April 24, 2015, in Tiffin, Iowa. Hide Caption 4 of 15 Photos: Carly Fiorina's political career Fiorina, right, poses for a selfie with Joe Koberna at the Johnson County Republicans Spaghetti Dinner at Clear Creek Amana High School on April 24, 2015, in Tiffin, Iowa. Hide Caption 5 of 15 Photos: Carly Fiorina's political career Fiorina speaks at the First in the Nation Republican Leadership Summit April 18, 2015, in Nashua, New Hampshire. Hide Caption 6 of 15 Photos: Carly Fiorina's political career Fiorina speaks during a forum on Capitol Hill March 16, 2015, in Washington. Fiorina spoke about what she calls the War on Women in politics. Hide Caption 7 of 15 Photos: Carly Fiorina's political career Fiorina delivers remarks at a discussion called "Welcoming Every Life: Choosing Life after an Unexpected Prenatal Diagnosis, focusing on caring for children with Down Syndrome," organized by the Heritage Foundation and the National Review Institute in Washington on January 20, 2015. Hide Caption 8 of 15 Photos: Carly Fiorina's political career Fiorina concedes defeat to her rival Sen. Barbara Boxer, D-California, during a news conference at her Irvine campaign headquarters on November 3, 2010, in Irvine, California. Hide Caption 9 of 15 Photos: Carly Fiorina's political career Fiorina, left, watches election results with granddaughter Kara Tribby, 7, in her hotel room at the Hyatt Regency Irvine, November 2, 2010, in Irvine, California. Hide Caption 10 of 15 Photos: Carly Fiorina's political career Fiorina, left, puts on headphones before participating in a radio debate with incumbent U.S. Sen. Barbara Boxer, D-California, in Washington, as co-moderator Gabriel Lerner, metro editor of La Opinion, does the same at local public-radio affiliate KPCC studios September 29, 2010, in Pasadena, California. Hide Caption 11 of 15 Photos: Carly Fiorina's political career Fiorina arrives for a news conference after participating in a debate with U.S. Sen. Barbara Boxer, D-California, in a radio debate hosted by La Opinion and public radio station KPCC on September 29, 2010, at the KPCC studios in Pasadena, California. Hide Caption 12 of 15 Photos: Carly Fiorina's political career Boxer, left, and Fiorina, center, greet moderator Randy Shandobil, right, after a debate on the campus of Saint Mary's College September 1, 2010, in Moraga, California. Hide Caption 13 of 15 Photos: Carly Fiorina's political career Fiorina, left, smiles with her husband Frank Fiorina, right, after casting their ballots at a polling place June 8, 2010, in Los Altos Hills, California. Hide Caption 14 of 15 Photos: Carly Fiorina's political career Fiorina greets supporters after announcing her candidacy for U.S. Senate at Earth Friendly Products packaging plant on November 4, 2009, in Garden Grove, California. Hide Caption 15 of 15

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.

Photos: Ben Carson's career in politics Photos: Ben Carson's career in politics Ben Carson attends the National Action Network (NAN) national convention at the Sheraton New York Times Square Hotel on April 8, 2015, in New York City. Hide Caption 1 of 13 Photos: Ben Carson's career in politics Carson speaks during the 41st annual Conservative Political Action Conference (CPAC) at the Gaylord International Hotel and Conference Center on March 8, 2014, in National Harbor, Maryland. Hide Caption 2 of 13 Photos: Ben Carson's career in politics Carson speaks to guests at the Iowa Freedom Summit on January 24, 2015, in Des Moines, Iowa. Hide Caption 3 of 13 Photos: Ben Carson's career in politics Carson is surrounded by supporters as he waits to be interviewed at the annual Conservative Political Action Conference (CPAC) at National Harbor, Maryland, outside Washington on February 26, 2015. Hide Caption 4 of 13 Photos: Ben Carson's career in politics Carson speaks at the South Carolina Tea Party Coalition convention on January 18, 2015, in Myrtle Beach, South Carolina. A variety of conservative presidential hopefuls spoke at the gathering on the second day of a three-day event. Hide Caption 5 of 13 Photos: Ben Carson's career in politics Carson delivers the keynote address at the Wake Up America gala event on September 5, 2014, in Scottsdale, Arizona. Hide Caption 6 of 13 Photos: Ben Carson's career in politics Carson speaks during the 41st annual Conservative Political Action Conference (CPAC) at the Gaylord International Hotel and Conference Center on March 8, 2014, in National Harbor, Maryland. Hide Caption 7 of 13 Photos: Ben Carson's career in politics Carson speaks during the National Prayer Breakfast at the Washington Hilton on February 7, 2013, in Washington. Hide Caption 8 of 13 Photos: Ben Carson's career in politics Honoree and director of pediatric neurosurgery at Johns Hopkins University, Carson poses with actor James Pickens Jr. at the Jackie Robinson Foundation Annual Awards Dinner on March 16, 2009, in New York City. Hide Caption 9 of 13 Photos: Ben Carson's career in politics Before his jump into conservative politics, Carson was known for his work as a neurosurgeon. Carson was awarded the Presidential Medal of Freedom by then-President George W. Bush on June 19, 2008. At that time, he was the director of pediatric surgery at Johns Hopkins Hospital in Baltimore, Maryland. Hide Caption 10 of 13 Photos: Ben Carson's career in politics In a story that garnered international attention, Carson was ready to separate a pair of 10-year-old Indian girls, Saba and Farah Shakeel, who are joined at the head in New Delhi, India. Here, he addresses a press conference at the Indraprashtra Apollo Hospital on October 4, 2005. Hide Caption 11 of 13 Photos: Ben Carson's career in politics Carson and a team of 20 specialists approved the procedure after studying the girls' brains; however, their parents were worried about their daughters' lives and did not give doctors permission to operate. The surgery did not happen. Hide Caption 12 of 13 Photos: Ben Carson's career in politics Carson observes the start of neurosurgery proceedings at the Raffles Hospital in Singapore on July 6, 2003. Carson and Dr. Keith Goh, left, performed a complex operation that was unsuccessful to separate 29-year-old twins Ladan And Laleh Bijani, who were joined at the head. Hide Caption 13 of 13

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

Photos: Moments from Marco Rubio's career Photos: Moments from Marco Rubio's career Florida Sen. Marco Rubio speaks in October 2013 at the Values Voter Summit, held by the Family Research Council in Washington. Hide Caption 1 of 20 Photos: Moments from Marco Rubio's career Sen. Mike Lee, left, and Rubio talk before a news conference to introduce their proposal for an overhaul of the tax code in March. Hide Caption 2 of 20 Photos: Moments from Marco Rubio's career Rubio, center, arrives in the House chamber ahead of Israeli Prime Minister Benjamin Netanyahu's address to a joint meeting of the U.S. Congress in March. Hide Caption 3 of 20 Photos: Moments from Marco Rubio's career Rubio speaks with the media after delivering remarks during the graduation of small business owners from the Goldman Sachs 10,000 Small Businesses program held in Miami in February. Hide Caption 4 of 20 Photos: Moments from Marco Rubio's career Rubio talks to aides in December before speaking on President Barack Obama's announcement about revising policies on U.S.-Cuba relations. Hide Caption 5 of 20 Photos: Moments from Marco Rubio's career Rubio, left, talks to Sen. Lindsey Graham prior to a news conference on Capitol Hill in July. Hide Caption 6 of 20 Photos: Moments from Marco Rubio's career Rubio talks to reporters in June after a closed door briefing on Capitol Hill. Hide Caption 7 of 20 Photos: Moments from Marco Rubio's career Rubio speaks to the media in front of a wall dedicated to the victims of the violence in Venezuela as he shows support for the Venezuelan community at a restaurant in Doral, Florida, in April 2014. Hide Caption 8 of 20 Photos: Moments from Marco Rubio's career Rubio speaks to the media at the Doral restaurant in April 2014. Hide Caption 9 of 20 Photos: Moments from Marco Rubio's career Rubio checks his phone in March as he arrives for a Capitol Hill news conference to introduce a proposal for an overhaul of the tax code. Hide Caption 10 of 20 Photos: Moments from Marco Rubio's career Rubio, left, is greeted as he arrives at a restaurant in Doral in February 2014. Hide Caption 11 of 20 Photos: Moments from Marco Rubio's career Rubio, left, and Florida Gov. Rick Scott speak to the media in Doral in February 2014. Hide Caption 12 of 20 Photos: Moments from Marco Rubio's career From left, Sens. Cory Booker, Rubio, Kristen Gillibrand and John McCain wait for Obama to deliver the State of the Union address in January 2014. Hide Caption 13 of 20 Photos: Moments from Marco Rubio's career Rubio addresses an event held by the American Enterprise Institute for Public Policy Research in January 2014. Hide Caption 14 of 20 Photos: Moments from Marco Rubio's career Paralympian Brad Snyder poses with Rubio during a Team USA Congressional visit in November 2013. Hide Caption 15 of 20 Photos: Moments from Marco Rubio's career Rubio speaks in November 2013 during a campaign stop for Virginia Attorney General Ken Cuccinelli, the Republican candidate for governor of Virginia. Hide Caption 16 of 20 Photos: Moments from Marco Rubio's career Rubio confers with McCain as U.S. Ambassador to Syria Robert Ford testifies before the Senate Foreign Relations Committee in October 2013. Hide Caption 17 of 20 Photos: Moments from Marco Rubio's career Rubio, center, speaks to members of the media as Sen. Ron Johnson, left, and Rep. Ron DeSantis listen during a news conference on Capitol Hill in October 2013. Hide Caption 18 of 20 Photos: Moments from Marco Rubio's career Rubio returns to the Capitol after meeting with Obama and other Republican leaders about the government shutdown in October 2013. Hide Caption 19 of 20 Photos: Moments from Marco Rubio's career Rubio speaks to an aide on Capitol Hill as he arrives for the weekly Senate Republican Policy Committee luncheon in September 2013. Hide Caption 20 of 20

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.