The White House launched the "It's On Us" campaign Friday, aimed at ending sexual assaults on college campuses. Several celebrities participate in the public service announcement. (YouTube/It's On Us)

When President Obama and Vice President Biden urged Americans on Friday to end sexual assaults on college campuses, the event included a standard feature for this White House: celebrities.

In a video, Cleveland Cavaliers forward Kevin Love, actors Jon Hamm and Connie Britton and other big names tell their fans to heed the president’s call, suggesting that people need to take responsibility for preventing rape among U.S. college students.

Stars have become an integral part of the White House messaging operation, from urging Americans to eat healthier to decrying the wage gap between men and women. While presidents have hobnobbed with celebrities for decades — Ronald Reagan once brought Princess Diana and John Travolta together on a dance floor — Obama and his aides have taken such relationships to a new level, systematically working with Hollywood actors, professional athletes and music stars to help raise money and promote the administration’s top domestic policy priorities.

The effort amounts to a separate publicity branch for the White House — at no extra charge. After several YouTube stars met with the president in late February to discuss the Affordable Care Act, they created 25 videos touting the law — garnering more than 32 million viewings.

White House officials see such efforts as a way to reach key demographic groups, especially those who eschew traditional political media. The celebrity push is in part an outgrowth of the administration’s campaign to enroll young people, African Americans, Latinos and women under Obama’s health-care law.

Funny or Die, the Emmy-award winning comedy website, has produced 11 short videos featuring a range of celebrities who work for free to plug President Obama's agenda. Here's a sample. (Jeff Simon/The Washington Post)

“Our purpose here is to meet people where they are,” White House senior adviser Valerie Jarrett said. “We’re extremely strategic in how we engage and deploy validators, and we’re very fortunate that people who have tremendous followings across the country are willing to be very effective messengers.”

Republicans, for their part, said it shows how the president is out of touch with everyday Americans.

“For years Obama and the Democrats have seemingly put more time and emphasis on celebrities than their policies and for years we’ve questioned the value in that priority,” said Republican National Committee spokeswoman Kirsten Kukowski, whose boss dubbed Obama the “Celebrity-in-Chief” during the 2012 campaign. “With 57 percent of the country disapproving of Obama and his policies, it’s a good thing he has celebrities behind him.”

But with Obama now well into his final term, his aides are less worried about whether bringing Hollywood types into his orbit could backfire politically.

Tommy Vietor, who served as the National Security Council spokesman during Obama’s first term, said that “if inviting George Clooney to the White House helps get press attention about Darfur, that’s clearly worth it to the president, and he could care less about cynical political attacks.”

Some of these efforts might take time to pay off. The creators of “Funny Or Die” produced a video starring Kristen Bell — “Mary Poppins Quits,” in favor of raising the minimum wage — that received nearly 3 million hits online, yet the issue remains moribund in Washington. And the president’s approval ratings among 18- to 29-year-olds — the target audience for much for this Hollywood-tinged outreach — has dropped to 43 percent.

Republicans have criticized Obama for his Hollywood connections and his own celebrity status from the start of his presidential candidacy. His 2008 rival, Sen. John McCain (R-Ariz.), ran an ad juxtaposing photos of Obama with Britney Spears and Paris Hilton, saying, “He’s the biggest celebrity in the world. But can he lead?”

Last month, Alabama Republican Party chairman Bill Armistead wrote in an e-mail to supporters: “Since 2009, the president has played more than 185 rounds of golf. Expensive vacation homes, fine dining, spontaneous trips, private concerts by the world’s top music artists; Obama’s life seems more like that of a celebrity than a president.”

But Republicans are not immune to the lure of famous people. House Majority Leader Kevin McCarthy (R-Calif.) let Kevin Spacey shadow him to learn about whipping votes for the Netflix series “House of Cards,” and he attended the series’s second-season premiere. The party had Clint Eastwood give an unscripted speech at its 2012 convention, regularly features country music stars and NASCAR drivers at GOP events, and calls on famous coaches such as Lou Holtz for pep talks behind closed doors.

Traditionally, presidents of both parties have enlisted celebrities at fundraisers and publicity events. Brookings Institution senior fellow emeritus Stephen Hess, who served under presidents Dwight Eisenhower and Richard M. Nixon, recalled how Ethel Merman helped raise money for Eisenhower (“probably because her husband was the president of an airline”) and how Democrats such as the Kennedys “had bushel baskets of starlets” in their orbit.

President Clinton appeared regularly with Hollywood stars, including Spacey, director Steven Spielberg and singer Barbra Streisand.

“Funny Or Die,” a comedic Web site, illustrates the Obama administration’s strategic approach to using celebrity supporters. The company’s president of production, Mike Farah, said in a phone interview that the site’s partnership with the administration began when he and others attended a White House meeting around the time of the 2013 White House Correspondents’ Association dinner.

“It just sounded like they needed a touch of help selling this dream,” said Farah, whose firm produced 11 videos in cooperation with Obama aides in the past year and has another set to be released soon. Outside of campaigns, he said, “government, as it’s set up, isn’t really about selling things to the public.”

Farah declined to say how much his company spent producing the videos, saying it folds the expenses into its monthly budget and focuses on producing “funny, topical content that’s relevant.” He added he hopes some of the videos make viewers think about today’s pressing political issues, but added, “I don’t have scientific evidence for this.”

Among the most successful collaboration so far was an episode of “Between Two Ferns with Zach Galifianakis,” a spoof talk show featuring an interview with Obama. The online video has been seen more than 24 million times and drove up traffic to the online federal health-care marketplace by 40 percent in a single day.

Some of the White House’s recruits have been surprised they made the list. Hannah Hart is a YouTube personality with 1.5 million subscribers who came to fame when a friend uploaded a video of her cooking while tipsy in her kitchen. When she got an e-mail inviting her to come to a meeting at 1600 Pennsylvania Ave., she recalled her response was, “Is this real?”

Hart has signed up for insurance on California’s health-care exchange and hosted a livestream event on the topic. When she realized she would be sitting across from Obama in the Roosevelt Room, she said, “beads of sweat began to form along my brow.” But she came away impressed with the exchange, posted a couple of videos, and said in an interview that she would be open to doing it again “on issues I feel strongly about.”

On rare occasions, celebrity endorsers fumble their message. Pop singer Lance Bass visited the White House in the spring to discuss health care — and went on a rant after he tweeted an incorrect address for HealthCare.gov. “Grow up people!” he wrote in disgust.

And of course many of these stars also help fill Democratic campaign coffers. In March 2013, Obama attended a Democratic National Committee reception at the New York City home of film studio executive Harvey Weinstein that also included stars such as Justin Timberlake and Steve Martin.

In July, he headlined a DNC fundraiser at the Los Angeles home of “Scandal” creator Shonda Rhimes, which was co-hosted by the show’s star, Kerry Washington.

DNC spokeswoman Rebecca Chalif said in a statement that star-studded events offer “ways to connect with our supporters.”

“Our well known supporters can be an invaluable asset to help us engage voters — especially voters who may not always turn out in midterms,” Chalif wrote.