President Biden’s campaign is working to reach across the generation gap to the tens of millions of predominantly younger voters on TikTok, where the challenges are daunting and the rewards difficult to track.

The obstacles range from anger over the war in Gaza to what social media experts describe as the unavoidably uncool nature of supporting the administration in power.

Mr. Biden, 81, joined the app owned by a Chinese company last month, in what was widely seen as an effort to communicate with voters under 30, among whom he has polled poorly for months. In interviews and surveys, those voters indicated an unawareness about his administration’s accomplishments, something a word of mouth campaign on TikTok could alleviate.

But navigating the platform and its more than 150 million users in the U.S. has involved confronting, usually in the comments sections of his own posts, some of the thorniest issues plaguing Mr. Biden’s re-election bid: disillusioned voters averse to politics, concerns about his age, outrage over the death toll in Gaza. Former President Donald J. Trump isn’t on the app, but his supporters are active. Adding to the puzzle, Mr. Biden’s aides are trying to sell his record on a platform his administration has argued poses a national security threat.

A bill to force TikTok to cut ties with its Chinese owner or otherwise face a ban in the U.S. is stalled in the Senate, but the president has said he’ll sign it if it passes — a position that has rankled even his staunchest young supporters.

“TikTok is sort of both driving, but ultimately reflecting, the culture. This is obviously a time when young people are feeling dissatisfied with the world they’re inheriting and not particularly in love with the institutions of power that they feel have let them down,” said Teddy Goff, a Democratic digital strategist. “I think President Biden actually has a totally amazing record, but saying ‘rah rah’ for the guys who are already in charge is not necessarily the coolest message for a group of 19-year-olds.”

Since the last presidential election, the video sharing app has exploded, becoming a dominant source for news and political discourse used by 56 percent of U.S. adults aged 18 to 34. The Biden campaign, since joining TikTok in February, has posted dozens of videos to its less than 300,000 followers.

Some showcase the president at retail stops and answering questions about the Super Bowl, while others feature campaign ads and clips from his State of the Union address. In an effort to re-engage voters galvanized by Mr. Trump in 2020, many posts center on the former president. A video highlighting Mr. Trump’s plans for a second term is among the campaign’s most-viewed videos.

Users frequently leverage TikTok features to add commentary to his posts in mocking ways. After the campaign posted a video of Mr. Biden criticizing Mr. Trump, saying, “Over my dead body will he cut social security,” some users responded with videos that called attention to the president’s age — receiving more views than the original.

Mr. Biden’s campaign has tried to use TikTok to address those larger voter concerns: In one video, Mr. Biden makes a quip about late night host Jimmy Fallon’s ratings after Mr. Fallon poked fun at Mr. Biden’s age. The derisive videos and comments are something that the campaign sees as normal when engaging on any social media platform.

“We see TikTok as one of many tools to reach voters in an increasingly fragmented media environment,” Lauren Hitt, a spokeswoman for Mr. Biden, said. “Thanks to record-breaking grass roots fund-raising, we’re reaching voters where they are and on every platform, from TikTok and Instagram to TV ads and door knocking.”

Much like the White House has partnered with social media influencers, Mr. Biden’s campaign plans to deploy TikTok creators to promote its message. But political activity is discouraged on TikTok compared with on other platforms: Community guidelines do not allow for paid political advertising, and users are banned from “receiving payment to create political content.”

What could resonate for Mr. Biden is a bit of an open question. In January, TikTok restricted access to a tool that measured the popularity of hashtags, making it harder to independently track how content performs.

Joan Donovan, a misinformation researcher who studies TikTok, said that it may be difficult for the campaign to reach unengaged audiences without facilitating a relationship with viewers on a platform that rewards authenticity.

Some younger Democrats like Rep. Alexandria Ocasio Cortez of New York and Rep. Jeff Jackson of North Carolina have gained sizable TikTok followings by conversationally explaining politics to viewers. The campaigns of Senator John Fetterman of Pennsylvania in 2022 and Senator Jon Ossoff of Georgia in 2020 successfully harnessed TikTok trends to reach potential voters in part because they were fresh faces to many.

Mr. Biden “has been a political animal for decades now, so the idea that you would rebrand and reintroduce him to the world just isn’t going to work,” Ms. Donovan said.

Annie Wu Henry, the architect of Mr. Fetterman’s TikTok strategy, said the landscape has changed even since his successful Senate bid, in part because of how many more people are using the app, and that “simply being on TikTok” is not enough.

“It doesn’t matter how good or fun or creative a TikTok is, if the person watching it is upset or doesn’t like the person being posted about,” she said.

Many young people using the app have been particularly upset by what they see as American complicity in Israel’s military campaign in Gaza. Images and videos of war proliferate on the app, as do posts exhorting people to punish Mr. Biden’s support for Israel by not voting for him in 2024, paying little regard to his administration’s push for a bilateral cease-fire agreement and more aid into Gaza. Pro-Palestinian users inundate his campaign’s posts with comments referencing Palestinians and Rafah, the Gaza city where more than one million people are sheltering and Israel has said it intends to attack.

“Biden recognizes the power that TikTok has to influence young voters. But he and the campaign don’t seem to understand that appealing to young voters has to come with a policy shift on Gaza and a number of issues,” said Aidan Kohn-Murphy, the 20-year-old founder of “Gen Z for Change,” a nonprofit coalition of TikTok creators. “You’re not going to win young voters back by posting a meme on TikTok.”

The “Gen Z for Change” account, which Mr. Kohn-Murphy began four years ago under a different name to promote Mr. Biden’s 2020 election bid, now regularly posts videos critical of the president to its 1.7 million followers.

Mr. Biden’s campaign has left communication on the war to the White House. Arab American leaders in Michigan rejected a meeting in January with the Biden campaign manager, expressing a desire to reach policy officials.

TikTok creators supporting Mr. Biden, such as Harry Sisson, a 21-year-old student who has posted videos extolling the president, have tried to fill the void. “When Donald Trump wins and destroys America because all these people decided to sit out, don’t complain,” he said in a November video, pushing back on posts that urged people to not support Mr. Biden.

In response, Mr. Sisson received a barrage of negative comments and videos attacking him, something he said happens often while championing the president.

Where even Mr. Sisson differs from the president is on the bipartisan congressional effort to force a sale of the app or have it banned, which he said would be “very bad” for Democrats. The White House recently privately lobbied talent agencies representing TikTok creators to emphasize that they wanted a divestment.

Mr. Trump, for his part, has backed off previous efforts to ban the app, and said he didn’t support the legislation.

Eric Wilson, a Republican digital strategist who encouraged candidates to join TikTok, said that data collected after the 2022 midterms showed more Republicans, especially young and Trump-aligned Republicans, regularly using the platform. Mr. Biden’s supporters are fighting for a voice against conservative users, whose content has ranged from praising the former president to highlighting subjects like the migrant crisis.

Mr. Wilson said that the key digital challenge for both presidential campaigns this year is combating “voter apathy and making sure that their supporters turn out.” Republican politicians have been more hesitant to join TikTok, he said, but can reach voters on platforms like Facebook, whereas young voters amenable to Democrats on TikTok are “difficult to reach elsewhere.”

But whether influencers can help Mr. Biden in a politically fraught environment remains to be seen. Emily Koh, a creator who recently partnered with a group that promotes progressive causes, said in an interview that she supported Democrats and wanted to be more politically active, but was disappointed by Mr. Biden’s stances on the TikTok legislation and the Gaza war.

Mr. Biden and his allies, Ms. Koh said, “have to do two things: They have to be willing to work with this new type of media, and they also have to actually do the things that we, as constituents, are requesting.”

“Even though there’s people that can make some really great content, it’s not like they can erase what’s actually happening,” she said.