First, there was Charli XCX’s post declaring Vice President Kamala Harris “is brat” on X. Then there was Beyonce’s approval of her song, “Freedom,” for Harris’s campaign use. And most recently, there was Megan Thee Stallion’s appearance at a Harris rally in Atlanta, alongside fellow musician Quavo.

Since Harris became the likely Democratic nominee at the end of July, celebrities have poured in to support and endorse her. Some have coordinated with the campaign, and others — like Charli XCX — expressed their backing on their own. Other notable names who’ve chimed in include billionaire Mark Cuban, rapper Cardi B, and actress Jane Fonda.

These endorsements have brought a new wave of star power to the presidential election, and could drive more attention, dollars and enthusiasm to the campaign. Whether they’ll persuade people who weren’t already open to Harris to consider her, however, is uncertain.

According to political scientists, celebrity endorsements tend to have “modest effects” in winning over voters, says Bowling Green State University professor David J. Jackson, who notes that they’re more likely to boost excitement for a candidate a voter may already be leaning toward, rather than sway someone to cross party lines.

Politicians often use celebrities in an attempt to energize key voting groups — and people who may be less engaged. Harris’s appearance alongside Megan Thee Stallion and Quavo in Atlanta, for instance, appeared dedicated to reaching younger voters as well as Black voters, both important groups that are expected to account for a notable proportion of the electorate this fall.

“Political candidates are heavily leaning on celebrities as a mechanism to attract the attention of this cycle’s youngest voting demographic: Generation Z,” says Melvin Williams, a professor of communications and media studies at Pace University.

According to a 2020 Pew study, Gen Z comprised roughly 10 percent of eligible voters that year, and about 45 percent of those voters were nonwhite. A major uptick in Gen Z turnout in 2020 was also critical to helping President Joe Biden secure the presidency, even though younger voters have historically turned out at lower rates than other age groups. And Black voters have historically been a significant proportion of Democrats’ base as well, with 92 percent of Black voters supporting Biden in 2020.

Beyond high-profile rallies, celebrities like actor George Clooney have given interviews and written social media posts announcing their backing for Harris. And others, like comedians Tiffany Haddish, Whoopi Goldberg, and Nick Offerman, have hosted virtual fundraising gatherings, like one dubbed Comics for Kamala, that took place this week. Such events highlight how celebrities can be key contributors to campaigns by driving donations and broader awareness.

Former President Donald Trump has seen some celebrities speak out on his behalf, too, including country singer Kid Rock and wrestler Hulk Hogan, both of whom appeared at the Republican National Convention. They respectively described him as a “badass,” “hero,” and “gladiator,” all seemingly in a bid to hype up his masculine credentials and energize the crowd ahead of Trump’s appearance at the event.

And model Amber Rose, who also spoke at the RNC, was among the participants booked with the apparent goal of expanding Trump’s appeal to Black voters, after he made marginal gains with the group in 2020. Trump doesn’t care if “you’re Black, white, gay, or straight, it’s all love,” she claimed. Like Harris, Trump has sought to cultivate ties with younger voters as well, appearing on podcasts with Gen Z influencers like Logan Paul and streamer Adin Ross — both of whom have young, male audiences.

If you’re one of the most famous, influential women in the world, you may be able to sway a presidential election a little. If not, the effect might be a bit more limited.

Oprah Winfrey’s support of former President Barack Obama in the 2008 Democratic primary is the rare example of a specific endorsement having a tangible, scientifically studied impact on candidate choice. According to a 2013 Northwestern University study, her endorsement — one of just a few political statements of support she’s made — translated to an uptick in turnout, donations, and approximately a million votes in favor of Obama.

A key caveat of that study is that it centered on a Democratic primary, when voters were choosing from candidates with the same party affiliation, rather than a general election, when candidates tend to have major partisan differences. Additionally, experts note that endorsements could provide voters with more useful information in a primary when there may be a broader mix of new and familiar options. In a general election, if the candidates are more well-established, endorsements could be less likely to offer novel insights.

“That was a different environment because that was a primary election between Democrats where Oprah weighed in to that contest,” University of Wisconsin political scientist Barry Burden previously told CBS 58, a regional affiliate in Wisconsin. “So everyone participating is essentially a Democrat or sympathetic to a Democrat and that’s where an endorsement could really matter.”

That case study, though, shows how a prominent celebrity could wield their cachet. Less powerful celebrities, meanwhile, still have the potential to have a narrower impact. They might strengthen a candidate’s connection with a specific age group or demographic, they could help drive people to turn out, and they could get more people to contribute their money.

“If you suddenly see it in your social media feed or on TikTok or wherever, and see your favorite celebrity has done an interview or had a conversation with a politician, that politician is much more likely to get traction just by having that entry into people’s attention spans,” Josephine Harmon, an assistant professor of political science at Northeastern University in London, previously told Northeastern Global News.

A Megan Thee Stallion endorsement could bolster Harris’s credibility among her listeners and add to her appeal given the singer’s popularity and clout. A fan who was already leaning Democrat could also be motivated to register to vote, or attend a rally, because of her endorsement.

That was likely the case with endorsements like those made by Taylor Swift in 2018 and 2020. In 2018, Swift endorsed Tennessee Democratic Senate candidate Phil Bredesen, and emphasized why she opposed then-Republican Senate candidate Marsha Blackburn due to her votes on the Violence Against Women Act and her stance against marriage equality.

Following Swift’s 2018 post, 65,000 people between the ages of 18 to 29 registered to vote, according to Vote.org, an uptick the nonprofit attributed to her post, noting that it may have galvanized people to get involved who wouldn’t have otherwise.

“Overall, celebrities would like to think they could influence voter behavior, but they are more valuable as fundraising tools and door-opening opportunities to their followers,” David Paleologos, director of the Suffolk University Political Research Center, told CBS 58.

In a close election like this one — 538’s polling average puts Harris less than 2 percentage points ahead of Trump nationally, as of Wednesday — celebrities, and such marginal gains, could nonetheless be important. “Even though the effects are generally thought of as modest, in elections that turn on a small number of votes in a handful of swing states, any effect could be significant,” Jackson told Vox.