WASHINGTON — When Robert De Niro showed up outside a Manhattan courthouse to decry former President Donald Trump as his New York hush money trial was winding down, it sparked a life-imitates-art screaming match with a nearby group of Trump supporters.

“You are gangsters!” De Niro, who starred in “Goodfellas” and won an Oscar for “The Godfather Part II,” shouted at the Trump backers, who responded with obscenities.

There are plenty more Hollywood storylines still to come in the 2024 campaign: Celebrities are increasingly lending their star power to President Joe Biden, hoping to energize their fans to vote for him in November and entice donors to pony up for his reelection effort.

On Saturday, A-listers George Clooney and Julia Roberts will team up with former President Barack Obama at a Biden fundraiser in Los Angeles, where the three will be interviewed by late-night talk show host Jimmy Kimmel. Roberts and Kimmel have already begun soliciting donations via text for Biden, who is skipping a weekend peace conference on Ukraine being held in Switzerland to attend the event.

Director Steven Spielberg is involved in storytelling efforts for the Democratic National Convention in August. Lenny Kravitz, Barbra Streisand and James Taylor have all performed for Biden donors.

Others who’ve sent fundraising emails, organized events or otherwise lent their support include actor Connie Britton, singer-songwriter Carole King, “Bridgerton” creator Shonda Rhimes, singer Christina Aguilera, actor Queen Latifah and actor Mark Hamill, who turned up in the White House briefing room last month to praise the president.

And, in another instance blurring lines between real life and make-believe, during a fundraiser at the home of actor Michael Douglas, Biden congratulated the star of the 1996 hit “The American President” on his fictional administration’s success.

For all the celebrity supporters, though, there’s little expectation they can determine votes. Rather, they are seen as having the ability to inject excitement that helps energize supporters.

Lexi Underwood, whose credits include the streaming series “Little Fires Everywhere,” calls acting a “contact sport” that allows her to interact with the public and makes her determined to use her influence responsibly. She has participated in a recent virtual “Students for Biden” event and traveled to Nevada to appear at campaign events focused on women’s health issues.

“I’m very fortunate to have certain eyes on me,” said Underwood, 20. “I feel really responsible to make sure that what I put out there, either people are being informed on things that they weren’t previously informed on, or that I’m motivating them to get out there and vote.”

Biden’s campaign says its chief focus is finding authentic and trusted messengers who can promote the president’s policy achievements and raise the alarm about GOP “extremism,” and that means deploying everyday supporters as well as famous ones.

It has produced ads featuring a Pennsylvania union worker, a Black entrepreneur in Detroit and women adversely affected by strict abortion limits in Texas.

Fai Nelson, a human resources worker who attended a recent Vice President Kamala Harris event in Prince George’s County, Maryland, said celebrity voices can make a difference “if they can touch the audience.”

Adrienne Elrod, who served as Biden’s 2020 director of surrogate strategy and operations, said famous Biden supporters often “will come forward with their own ideas” on how to help the campaign and what issues they’d like to focus on.

De Niro has taken on an increasingly prominent role in Biden’s campaign. Before his confrontation with the Trump supporters, the actor held a news conference calling the former president a “clown.”

He’s also attended Biden fundraisers and narrated a campaign ad accusing Trump of having “snapped” after he lost the 2020 election.

Karoline Leavitt, a spokesperson for the former president’s campaign, said, “The only people in America who support Joe Biden’s failing campaign are elitist Hollywood celebrities,” adding that Trump “speaks for the forgotten men and women of this country.”

Trump has his own list of celebrity endorsers, which includes musicians Kid Rock and Ted Nugent, media personality Caitlyn Jenner, comedian Roseanne Barr, and actors Dennis Quaid and Jon Voight.