do celebrities matter in the US election?

When Kamala Harris held a town hall for supporters in Michigan on Thursday night, she was joined on stage by an icon of American entertainment culture: Oprah Winfrey.

Winfrey, the 70-year-old media mogul best known for her long-running talk show, has largely shied away from the political spotlight in recent years. Despite being unaffiliated with either of the two main political parties, she made a surprise appearance at the Democratic National Convention in Chicago last month, endorsing Harris’s bid for the White House and calling on viewers to “choose common sense over nonsense”.

On Thursday night, she interviewed Harris before an in-person audience of about 400 people. Hundreds of thousands more watched a livestream from home.

“This grassroots people-powered movement behind Kamala Harris has unleashed a unifying force unlike anything we’ve seen in politics in a very long time,” Winfrey said. “I know lots of people are feeling it, because it actually is hope and joy rising.”

Winfrey is just one of a constellation of big stars with millions of fans who have announced their support for Harris and her running mate, Tim Walz. A number of others have come out for Donald Trump.

But the jury is out over whether celebrity endorsements actually boost a candidate’s chances at the ballot box.

There are some signs that Winfrey’s support could improve the vice-president’s chances of winning the White House in November.

The star, whose product recommendations used to drive huge sales for companies, made her first political endorsement in 2008, when she supported then-senator Barack Obama in that year’s Democratic presidential primary.

Academics at Northwestern University and the University of Maryland later estimated that her endorsement was responsible for 1mn additional votes for Obama, particularly among women.

The surprise endorsement from Taylor Swift, the world’s biggest pop star, minutes after last week’s presidential debate ended is also expected to move the dial in Harris’s favour.

Swift — who earlier in her career shied away from wading into politics — wrote on Instagram that she was voting for Harris “because she fights for the rights and causes I believe need a warrior to champion them”.

The 34-year-old megastar signed her post “childless cat lady” — a thinly veiled reference to Trump’s running mate JD Vance, who had lamented that the country was being run by “childless cat ladies”. She included a link to the website of non-profit group Vote.org for her 272mn followers to register to vote.

Vote.org later reported receiving more than 35,000 new voter registrations through the link.

A Monmouth University poll on Thursday found that 76 per cent of registered voters said they had heard about Swift’s endorsement.

“She is probably the most recognised person on the planet at the moment,” said Michael Platt, a professor of marketing at the University of Pennsylvania’s Wharton School of Business.

But other surveys suggest that while the vast majority of Americans know who Swift will be voting for, most are not swayed by her message.

An ABC News/Ipsos poll published on Sunday found that 81 per cent of voters said the endorsement would make no difference in how they cast their ballots, and just 6 per cent said it would make them more likely to vote for Harris. Another 13 per cent said it would make them less likely to support the vice-president.

The news certainly had an impact on Harris’s opponent. Trump lashed out at the news, posting on his Truth Social platform on Sunday: “I HATE TAYLOR SWIFT!”

Still, Democrats have welcomed the endorsement, which Harris campaign officials said came as a surprise to the vice-president and her team.

They argue that in a presidential election likely to be decided on the margins, every vote counts, especially if Swift and other celebrities can motivate younger voters and others who are less likely to show up at the polls.

“We live in this highly fragmented media environment in which most folks have made up their mind about who they are voting for,” said a Harris campaign official. “It is going to come down to a pretty small number of voters that will decide this election.”

This week singer-songwriter Billie Eilish and her brother Finneas O’Connell also endorsed Harris, posting an Instagram video urging their more than 120mn followers to register and back the vice-president and her running mate.

The Harris campaign’s Instagram account commented on the post with a reference to one of Eilish’s songs, writing: “Birds of a feather” with a heart emoji.

Some Democrats caution against being seen as too enmeshed with celebrity culture, especially as the party tries to pitch itself as a champion of working-class Americans. Others point out that celebrity endorsements can only take a candidate so far.

Hillary Clinton’s 2016 bid for the White House was a star-studded affair — she was even joined on stage by the notoriously press-shy Jay-Z and Beyoncé on the eve of the election, yet lost to Trump.

The pop and hip-hop power couple have yet to weigh in on the 2024 race, though Beyoncé has allowed Harris to use her anthem “Freedom” in advertisements and on the campaign trail.

“We are mindful that this isn’t a celebrity-forward campaign,” the Harris campaign official said. “Our approach here is that we will utilise the celebrity support . . . to generate a moment of excitement or reach a certain community.”

Trump, who was a television star as the host of The Apprentice before turning to politics, has also welcomed celebrity endorsements for his bid for the White House.

He gave primetime slots to rapper Kid Rock, professional wrestler Hulk Hogan and model Amber Rose at the Republican National Convention in July.

But the former president has bristled at A-list backers of Harris other than Swift.

When actor George Clooney made waves this summer for urging President Joe Biden to suspend his re-election bid in a New York Times op-ed, Trump declared in a post on Truth Social: “Clooney should get out of politics and go back to television. Movies never really worked for him!!!!”

The actor responded this week in an appearance on late-night television. “I will if he does,” he pledged. “That’s a trade-off I’d do.”