But can Harris really be its secret weapon, and defy polls that show US voters still aren't convinced she's the right person to be a heartbeat away from the Oval Office?
Harris made US history when she became the first female, Black and South Asian vice president in 2021 -- but then spent much of Biden's first term getting often low-profile tasks from her boss.
Yet things have changed drastically since the 2024 campaign kicked into high gear.
Harris has become the face of the White House's efforts to target what she has called "Trump abortion bans" in more than 21 US states, an issue Democrats see as a vote winner.
"This is a fight for freedom," Harris said Wednesday to cheers in Jacksonville, Florida, as she slammed the state's new ban on abortions after six weeks of pregnancy.
"She is charging across the country, inspiring the fight for women," the city's mayor Donna Deegan told the event, which finished with a show by a band from a historically Black university.
Aides said Harris had been taking the lead on the issue since the first reports two years ago that the US Supreme Court would overturn the half-century-old nationwide right to abortion.
Biden's campaign is using Harris to target the coalition of voters that delivered victory in 2020 but now seems to be fracturing -- particularly Black voters.
She reached out to Black male voters in Atlanta this week, launching a tour of battleground states to promote economic policies the administration says will help them.
Then there's Gaza, an ever tougher issue for Biden as protests against his support for Israel's military operation roil US campuses.
- 'Momala' -
Harris, who hails from a family with a background of rights activism, has often seemed a step ahead of her boss when it comes to rhetoric on Gaza.
It was the vice president who -- in a March speech at an Alabama site that was significant in the US civil rights struggle -- first called for an immediate ceasefire and delivered the administration's toughest language to date on the plight of Palestinian civilians.
As screens on Air Force Two played images of pro-Palestinian campus protests being broken up by police as she headed back from Florida, aides insisted she and the president were on the same page.
Despite Harris's newly prominent role, she and her staff remain wary.
She suffered years of bad press and criticism from Republicans over everything from alleged gaffes to the way she laughs.
And while she often comes to the back of her plane to talk to journalists off the record -- unlike Biden -- she still rarely gives interviews.
Earlier this week, Harris was mocked after she told chat show host Drew Barrymore her family sometimes call her "Momala" -- leading Barrymore to reply, "We need you to be Momala of the country."
While Biden had a series of substantial roles while he was vice president to Barack Obama, Harris has struggled to find one, and faced criticism in particular during a spell dealing with migration from Central America.
Polls meanwhile seem to back up the fact that voters have a problem with Harris and Biden alike.
She has an approval rating of just 38.5 percent, just shy of her boss's already low 38.9 percent, according to polling aggregator FiveThirtyEight.
But the US vice president's job is famously tough.
Despite being "not worth a bucket of warm spit," in the words of one of Franklin D. Roosevelt's vice presidents, John Nance Garner, it also involves being an ever-ready understudy in case the president is incapacitated.
Thomas Whalen, an associate professor of social sciences at Boston University, said Harris was doing a good job on the campaign trail.
"Particularly on the abortion issue, she's been strategically deployed," Whalen told AFP.
"Given polls are showing that African American voters are skeptical about supporting Biden for another go round, she's going to be even more important," he said.
"Right now, she seems to be doing an effective job."
