Biden endorsed Harris to take his place as the Democratic presidential nominee in the upcoming election on Sunday, writing that his decision to choose her as his running mate in 2020 was “the best decision I’ve made” in a post shortly after announcing he was leaving the race. The Biden campaign has also quietly tested whether Harris would be a viable choice against presumptive Republican nominee Donald Trump in a survey of voters, the New York Times reported last week.

Harris’ election as vice president four years ago marked a series of historic firsts, making her the highest-ranking female elected official in U.S. history as well as the highest elected Black and Asian official.

But Harris faces a challenge common to many vice presidents—of forging her own distinct identity after playing the No. 2. In a statement on Sunday, Harris said she intends “to earn and win this nomination.”

During Biden’s first term, the 59-year-old has taken on some of the Biden administration’s toughest assignments, from the U.S.-Mexico border, to abortion rights, to voting rights. 

Harris has become the face of the Democratic Party’s push for abortion rights since Roe v. Wade was overturned in 2022. In January she kicked off a “Fight for Reproductive Freedoms” tour this year during which she became the first sitting VP to visit an abortion clinic. She has backed federal legislation that would guarantee a national right to abortion.

Harris has also led the Biden administration’s efforts to expand voting rights, including helping craft legislation that was ultimately stymied in the Senate.

A pro-business ‘centrist’

Her record on economic issues, however, is murkier—a potential liability at a time when Americans cite inflation and the economy as top issues.

As the VP, Harris can take credit for casting a record number of tie-breaking votes in the Senate to pass the Biden Administration’s priorities, including the Inflation Reduction Act, which funneled billions into clean-energy initiatives and codified lower prices for some prescription drugs.

Her record as California’s attorney general could bolster her standing against Trump and appeal to moderate voters.

“The business community, especially the tech/VC community are exhilarated over this choice,” Jeffrey Sonnenfeld, senior associate dean for leadership studies at the Yale School of Management, told Fortune via email. “She is a confirmed centrist and strong prosecutor of the rule of law. Business leaders are especially worried about Trump’s violation of the rule of law in favor of the law of rulers.”

But Harris has also received criticism for her approach to some hot-button issues, particularly on immigration. It took her months to visit the US-Mexico border, even after being tapped by Biden to spearhead the administration’s response to the crisis. Her trip to Guatemala and Mexico in March was overshadowed in the press by an interview with Lester Holt of NBC News where she “awkwardly downplayed the urgency” of the visit, The Washington Post said. She hasn’t visited the border since. 

Several Republicans used her perceived failure at the border as ammunition at the 2024 Republican National Convention. In her speech, Former United Nations Ambassador Nikki Haley warned of “four more years of Biden or a single day of Harris.” She cast Harris’ performance – in some eyes, unfairly – as failing to uphold one of her only duties as vice president. 

“Kamala had one job — one job — and that was to fix the border,” Haley said. “Now imagine her in charge of the entire country?”

Democrats have also expressed concerns about her sometimes gregarious sense of humor, which come at moments that are sometimes criticized as cringeworthy.