As concerns grew around 81-year-old Mr Biden’s ability to beat Trump in November, some major donors paused funds when the president’s poll numbers were falling in swing states, including Michigan.
Meanwhile, Trump, 78, also saw a boost in personal ratings, external after a gunman attempted to assassinate him at a rally in Pennsylvania last month.
But after Mr Biden stepped down, Ms Harris received a record level of donations - $81m (£63m) within 24 hours. Since then, a Morning Consult poll released on Tuesday showed Harris’s approval rating at 50%, up from 43% a week previously, and a separate poll from Reuters/Ipsos found Ms Harris was supported by 43% of registered voters, and Trump supported by 42%.
Some Democratic campaigners in Michigan say that her background as a black woman has helped Ms Harris reach some voters. Her Indian heritage - and the fact she is significantly younger than both Mr Biden and Trump - are also said to boost her appeal to some of the electorate.
Greg Bowens, a member of the executive board of the NAACP in Grosse Pointe, said there is “excitement in the air” in Detroit. He added this hasn’t been seen in Detroit - Michigan's largest majority African-American city - since Barack Obama, the first black president.
“She has electrified black and brown folks,” he said.
While an apparent wave of enthusiasm grows among some Democratic voters, Ms Harris has been subjected to attacks based on her gender and background.
A 2021 video of Trump’s running mate JD Vance resurfaced has resurfaced, with the Republican criticising the political left - including Ms Harris - for being full of “childless cat ladies with miserable lives”. The remark was criticised widely, including by actor Jennifer Aniston, but they were seized on by some conservative figures on social media, who argued that Ms Harris is less suitable to be president because she lacks a stake in the future. Ms Harris is step-mother to her husband’s two children.
More generally, female candidates face more superficial criticisms than male politicians about how they look, how they carry themselves and how they speak, said Ms Paul, the Fems for Dems leader who helps encourage women to vote and run for office.
It’s a point seemingly not lost on many voters - a Pew Research Center poll, external from September 2023 said 62% of Americans believed there was too much of a focus on female candidates’ appearances, versus 35% for male candidates.
Female politicians of colour are targeted more than their white male counterparts, said Nazita Lajevardi, a Michigan State University political science professor. “Women of colour politicians face attacks that are gendered and raced at the same time,” she said. “They report experiencing more verbal attacks, more online abuse."
Female, black public figures can be subjected to scrutiny of their past sexual history, said Jamil Scott, an assistant professor of government at Georgetown University. Images have circulated on social media with criticisms of Ms Harris’ past romantic partners. Whatever the motivation for circulating these images, Ms Harris has been married to Second Gentleman Doug Emhoff for 10 years.
Ms Scott said that as a female politician, Ms Harris will also likely be forced to walk a tightrope where she is perceived as strong in attacking her Republican rival, but doesn’t risk being seen as angry.
“We want women to be tough as candidates, but then we don't want them to be too tough,” she said.
Ms Scott pointed to Hillary Clinton - the first US major party female presidential candidate - who was perceived by some to be unlikeable and too aggressive in her attacks against Trump in 2016.
Trump attempted to exploit this sense, famously calling Ms Clinton a “nasty woman”.
While Ms Harris's background and stance on abortion may appeal to some, they do not guarantee support among left-leaning voters.
Tressa Johnson, a 31-year-old liberal voter from Grand Rapids, believes Ms Harris’s policy stances are what make her undesirable - not her ethnicity or gender. She says the vice-president’s past as a tough-on-crime prosecutor and the Biden administration’s limited criticism of Israel’s actions in Gaza make her a poor candidate.
“People just want to go, ‘Look, she's a woman of colour,’” said Ms Johnson, who plans to vote for Green Party candidate Jill Stein. “I just want a competent person that cares about the working class people in this country.”
