(CNN) With her poll numbers hitting a stubborn plateau, the third Democratic presidential debate may become a key moment for Sen. Kamala Harris to recapture the momentum her candidacy has lost in recent weeks, multiple sources inside and outside the campaign said.

"This is a crucial month for her in fundraising and debates," one Harris adviser said. "The campaign can't survive on glimpses and glimmers.

"If she doesn't do well, it's harder to reverse the shift," the source added.

Harris' team hopes to surface a different side of the California senator and former prosecutor: one that emphasizes aspects of her personality that are more often seen in unscripted moments on the campaign trail than in Harris' biggest televised moments on the national stage, according to multiple campaign aides.

The objective: defend Harris' record while also appearing presidential by staying above the fray and avoiding messy fights on the stage. Aides want Harris to continue opening up about her personal experiences, channeling interactions with voters where her aides believe she has most shined on the campaign trail -- and countering a perception that she is overly rehearsed and planned.

Harris' toughness and ability to "prosecute" a case against a second term for President Donald Trump has been the centerpiece of her appeal to voters.

Whether it is Harris' questioning of Trump administration officials or Supreme Court Justice Brett Kavanaugh during congressional testimony, the campaign has been eager to embrace Harris' persona as a candidate who is "tough" enough for a general election fight against Trump.

But at Thursday's primary debate, her campaign hopes she will lean into an earlier theme in her campaign -- being a "joyful warrior," according to a source with direct knowledge of the strategy.

"Her entire tagline as being a joyful warrior is something that people respond to really well on the campaign trail, and that's something they want people to see on the debate as well," that aide said.

For Harris, the terrain of the primary race has suddenly threatened to morph into quicksand. Her poll numbers have stagnated in the mid-single digits after her spike following the June debate. When CNN released an August poll that showed Harris had fallen back down to 5% nationally, a Harris campaign adviser described it as "the lowest point of the campaign thus far.

"I think sometimes she feels like she's putting a guard up. Like it's more of a show, you know what I mean?" Yamaisi Errasti, a 22-year old University of South Carolina Graduate student who is still an undecided voter, told CNN. "It's just trying to pursue or portray a certain image of herself, as opposed to her authentic self."

Ian Sams, Harris's national press secretary, said the senator's focus in this debate will be on pitching herself as a "unifying" candidate.

"Kamala will take on Donald Trump directly and will focus on bringing the country together by defeating him and unifying Americans around solutions to our common challenges," Sams said. "She'll make the connection between his hatred and division and our inability to get things done for the country."

Photos: Vice presidential nominee Kamala Harris Photos: Vice presidential nominee Kamala Harris US Sen. Kamala Harris speaks during an economic forum in Las Vegas in April 2019. Hide Caption 1 of 42 Photos: Vice presidential nominee Kamala Harris A young Harris is seen with her mother, Shyamala, in this photo that was posted on Harris' Facebook page in March 2017. "My mother was born in India and came to the United States to study at UC Berkeley, where she eventually became an endocrinologist and breast-cancer researcher," Harris wrote. "She, and so many other strong women in my life, showed me the importance of community involvement and public service." Hide Caption 2 of 42 Photos: Vice presidential nominee Kamala Harris Harris and her younger sister, Maya, pose for a Christmas photo in 1968. Hide Caption 3 of 42 Photos: Vice presidential nominee Kamala Harris Harris rides a carousel in this old photo she posted to social media in 2015. Her name, Kamala, comes from the Sanskrit word for the lotus flower. Harris is the daughter of Jamaican and Indian immigrants and grew up attending both a Baptist church and a Hindu temple. Hide Caption 4 of 42 Photos: Vice presidential nominee Kamala Harris Harris tweeted this photo of her as a child after referencing it during a Democratic debate in June 2019. During the debate, she confronted Joe Biden over his opposition many years ago to the federal government mandating busing to integrate schools. "There was a little girl in California who was bussed to school," she tweeted. "That little girl was me." Hide Caption 5 of 42 Photos: Vice presidential nominee Kamala Harris Harris got her bachelor's degree from Howard University in Washington, DC. Hide Caption 6 of 42 Photos: Vice presidential nominee Kamala Harris Harris graduates from law school in 1989. "My first grade teacher, Mrs. Wilson (left), came to cheer me on," Harris said. "My mom was pretty proud, too." Hide Caption 7 of 42 Photos: Vice presidential nominee Kamala Harris Harris is joined by San Francisco Mayor Gavin Newsom, left, and the Rev. Cecil Williams, center, for a San Francisco march celebrating Martin Luther King Jr. in January 2004. Harris was the city's district attorney from 2004 to 2011. Hide Caption 8 of 42 Photos: Vice presidential nominee Kamala Harris Harris speaks to supporters before a "No on K" news conference in October 2008. The San Francisco ballot measure Proposition K sought to stop enforcing laws against prostitution. It was voted down on election day. Hide Caption 9 of 42 Photos: Vice presidential nominee Kamala Harris Harris looks over seized guns following a news conference in Sacramento, California, in June 2011. Harris became California's attorney general in January 2011 and held that office until 2017. She was the first African-American, the first woman and the first Asian-American to become California's attorney general. Hide Caption 10 of 42 Photos: Vice presidential nominee Kamala Harris Harris attends the Democratic Party's state convention in February 2012. Hide Caption 11 of 42 Photos: Vice presidential nominee Kamala Harris Harris watches California Gov. Jerry Brown sign copies of the California Homeowner Bill of Rights in July 2012. Hide Caption 12 of 42 Photos: Vice presidential nominee Kamala Harris Harris speaks on the second night of the 2012 Democratic National Convention. Hide Caption 13 of 42 Photos: Vice presidential nominee Kamala Harris In May 2013, Harris and California Highway Patrol Commissioner Joe Farrow place a wreath honoring Highway Patrol officers who were killed in the line of duty. Hide Caption 14 of 42 Photos: Vice presidential nominee Kamala Harris Harris officiates the wedding of Kris Perry, left, and Sandy Stier in June 2013. Perry and Stier were married after a federal appeals court cleared the way for California to immediately resume issuing marriage licenses to same-sex couples. Hide Caption 15 of 42 Photos: Vice presidential nominee Kamala Harris Harris is flanked by her husband, Douglas Emhoff, and her sister, Maya. Next to Maya Harris is Maya's daughter, Meena, and Maya's husband, Tony West. Hide Caption 16 of 42 Photos: Vice presidential nominee Kamala Harris Harris receives a gift from supporters in January 2015, after she announced plans to run for the US Senate. Hide Caption 17 of 42 Photos: Vice presidential nominee Kamala Harris Harris speaks during a news conference in February 2015. Hide Caption 18 of 42 Photos: Vice presidential nominee Kamala Harris Harris, as a new member of the Senate, participates in a re-enacted swearing-in with Vice President Joe Biden in January 2017. She is the first Indian-American and the second African-American woman to serve as a US senator. Hide Caption 19 of 42 Photos: Vice presidential nominee Kamala Harris Harris talks with former US Sen. Bob Dole on Capitol Hill in January 2017. Hide Caption 20 of 42 Photos: Vice presidential nominee Kamala Harris Harris attends the Women's March on Washington in January 2017. Hide Caption 21 of 42 Photos: Vice presidential nominee Kamala Harris Harris speaks to Fatima and Yuleni Avelica, whose father was deported, before a news conference on Capitol Hill in March 2017. Hide Caption 22 of 42 Photos: Vice presidential nominee Kamala Harris Harris greets a crowd at an event in Richmond, Virginia, in October 2017. Hide Caption 23 of 42 Photos: Vice presidential nominee Kamala Harris In November 2017, Harris was among the lawmakers on the Senate Intelligence Committee grilling Silicon Valley giants over the role that their platforms inadvertently played in Russia's meddling in US politics. Hide Caption 24 of 42 Photos: Vice presidential nominee Kamala Harris Harris and her husband attend a Golden State Warriors basketball game in May 2018. Hide Caption 25 of 42 Photos: Vice presidential nominee Kamala Harris Harris attends a rally with, from left, California Secretary of State Alex Padilla, gubernatorial candidate Gavin Newsom, and Newsom's wife, Jennifer, in May 2018. Newsom won the election in November. Hide Caption 26 of 42 Photos: Vice presidential nominee Kamala Harris Harris speaks with US Sen. Cory Booker during the confirmation hearing for Supreme Court nominee Brett Kavanaugh in September 2018. Hide Caption 27 of 42 Photos: Vice presidential nominee Kamala Harris Harris presses Kavanaugh during his confirmation hearing. Hide Caption 28 of 42 Photos: Vice presidential nominee Kamala Harris Harris arrives with staff for a Senate Judiciary Committee hearing in September 2018. Hide Caption 29 of 42 Photos: Vice presidential nominee Kamala Harris Harris reads from her children's book "Superheroes Are Everywhere" during a book signing in Los Angeles in January 2019. She also released a memoir, "The Truths We Hold: An American Journey." Hide Caption 30 of 42 Photos: Vice presidential nominee Kamala Harris A person holds a Harris poster during the Women's March in Los Angeles in January 2019. Hide Caption 31 of 42 Photos: Vice presidential nominee Kamala Harris Harris holds her first presidential campaign rally in January 2019. She had announced her presidential bid a week earlier on Martin Luther King Jr. Day. Hide Caption 32 of 42 Photos: Vice presidential nominee Kamala Harris Harris speaks during her CNN town-hall event, which was moderated by Jake Tapper in Iowa in January 2019. Hide Caption 33 of 42 Photos: Vice presidential nominee Kamala Harris Media members photograph Harris and the Rev. Al Sharpton as they have lunch at Sylvia's Restaurant in New York in February 2019. Hide Caption 34 of 42 Photos: Vice presidential nominee Kamala Harris Harris confronts former Vice President Joe Biden, left, during the first Democratic debates in June 2019. Harris went after Biden over his early-career opposition to federally mandated busing. Hide Caption 35 of 42 Photos: Vice presidential nominee Kamala Harris Harris rides her campaign bus in Iowa in August 2019. Hide Caption 36 of 42 Photos: Vice presidential nominee Kamala Harris Harris and Biden greet each other at a Detroit high school as they attend a "Get Out the Vote" event in March 2020. Harris had dropped out of the presidential race a few months earlier. Hide Caption 37 of 42 Photos: Vice presidential nominee Kamala Harris From left, Harris, Senate Minority Leader Chuck Schumer and US Sen. Cory Booker stand near a Capitol Hill statue of abolitionist Frederick Douglass during a June 2020 event commemorating the life of George Floyd. Floyd, an unarmed Black man, was killed in police custody in Minneapolis. Hide Caption 38 of 42 Photos: Vice presidential nominee Kamala Harris Biden calls Harris from his Delaware home to inform her that she was his choice for vice president. Hide Caption 39 of 42 Photos: Vice presidential nominee Kamala Harris Biden listens as Harris speaks during their first campaign event as a presidential ticket. Hide Caption 40 of 42 Photos: Vice presidential nominee Kamala Harris Harris and Biden sign paperwork to officially get on the ballot in all 50 states. Hide Caption 41 of 42 Photos: Vice presidential nominee Kamala Harris Harris delivers a speech as she formally accepts the nomination at the Democratic National Convention. "Let's fight with conviction," Harris said in her speech. "Let's fight with hope. Let's fight with confidence in ourselves and a commitment to each other. To the America we know is possible. The America we love." Hide Caption 42 of 42

Her campaign is also seeking to confront a challenge that Harris uniquely faces as a black woman running for president: rounding out her image as both competent and presidential, while also revealing more of her personal side.

"It's a black woman running for president of the United States," said Bakari Sellers, a Harris surrogate and CNN political commentator. "And I think the bar is going to be higher, and she has to be able to reach that, and I'm sure she will.

"So I think a lot of it is just navigating that," he added.

Still, some Harris aides downplayed the significance of this debate for her, arguing that voters are just beginning to pay attention to the race, and there is still time for Harris to capture their attention.

"We're now in the part of the race where voters start kicking the tires," one campaign senior official said. "We're now getting into the meat of the campaign."

Past performances

June's debate provided Harris the high point of her campaign. Harris took Joe Biden to task for his remarks about two segregationist senators, in which he cited them as examples of colleagues he could work with during an era where "at least there was some civility" in the Senate. Harris called the words "hurtful," then recalled how, as a child, she was bused to school in a local effort to desegregate districts.

"That little girl was me," she told Biden.

The attack proved effective in getting the attention of some Democratic voters, but campaign aides, advisers and donors say that the aftermath has been complex. She experienced a bump in both polls and fundraising afterward.

But one Harris fundraiser complained that the attack backfired because it now looks more like a premeditated ambush with the campaign even printing T-shirts with Harris' line "that little girl was me." The T-shirt and preparation felt "staged" and "prosecutorial," more like a courtroom act, the fundraiser said.

The days following Harris' performance were inconsistent. She struggled to clearly explain whether she would support federally mandated busing in current times when pressed by reporters, prompting a heated back and forth between Biden, Harris and their surrogates over whether Harris and Biden actually agree on the very issue she used to attack the former vice president.

Aides described Harris's second debate performance in July as a wash -- it was neither disastrous for her candidacy nor was it particularly helpful.

But the most damaging moment came when Rep. Tulsi Gabbard levied an attack, that many of Harris' allies described as predictable, on Harris' prosecutor record.

Gabbard attacked Harris' record as California attorney general, in a string of accusations, some of which were later deemed by fact checkers to be false and misleading . Even though the campaign saw the Gabbard attack coming, Harris failed to effectively halt or avert it.

Aides acknowledged that Harris was not prepared and didn't effectively shut down the attacks on the stage.

In rolling out her criminal justice plan this week, the campaign wants the senator to be able to defend her record and refocus the criticism Harris faced on her plan to reform the system. Harris has also faced more questions about the very critiques levied at her by Gabbard and criminal justice reform activists, especially in the area of legalizing marijuana and the disproportionate rate of people of color who are convicted.

"Emotionally, it's hurtful," she told the New York Times about the criticism coming from young black activists.

Taken together, the two moments -- Harris's moment with Biden and the exchange with Gabbard -- portrayed Harris as eager to go on the attack on other candidates' records but unable to defend her own.

This time, however, there will be less of a focus of pitting Harris against any of the other candidates on the stage, and far more focus on painting a clearer picture for voters of who she is.

"I would want to see more about her personality," said Ivon Garcia, of Rockville, Maryland, told CNN. "I personally don't know much about Harris right now."

Aides are watching for other dynamics on the stage, as well. They're zeroing in on how Biden and Massachusetts, Sen. Elizabeth Warren interact and if Warren becomes a bigger target from the field, given her rise in the polls. Harris insiders say Warren is increasingly viewed as the candidate who poses the biggest concern to Harris because her support has continued to grow at a gradual, but constant rate.

"That suggests Warren's support is far less likely to collapse," a Harris campaign adviser said.