President Biden is discovering that passing one of the most ambitious legislative agendas in recent American history may have been the easy part. Persuading Americans that he deserves a second term may be far more difficult.

Confronting low approval ratings and a neck-and-neck race against former President Donald J. Trump, Mr. Biden is now racing to tell voters about his accomplishments, in ways big and small.

Road signs that promote his legislation are going up at construction projects financed by his $1 trillion infrastructure bill and at factories where jobs are being created by his $280 billion CHIPS and Science Act. Mr. Biden has affixed his name to emails telling Americans with student debt that their loans were being forgiven. And he is traveling to battleground states to sit down with voters who have benefited from his policies.

Democrats traditionally have been “the party of the abstract, and we need to be the party that humanizes things,” said Gov. Phil Murphy of New Jersey, a Biden ally who believes the president has the skill set to do just that. “He personally is so good at this, putting his arm — figuratively and literally — around the American people and saying, ‘Hey, listen, I feel your pain.’”

But Mr. Biden faces a host of challenges in reaping the credit that he feels he deserves as he seeks re-election to the White House.

Polling shows that a majority of Americans disapprove of his job performance. Many Americans say they benefited more from the policies of Mr. Trump. Most concerning for Mr. Biden, his support remains underwhelming among key parts of the Democratic coalition, including Black and Hispanic Americans and younger voters — the people many of his efforts were designed to help.

Some of that negativity can be attributed to the 81-year-old president’s age, the lingering effects of the pandemic and improved views of Mr. Trump, a phenomenon that is common after presidents leave office. The war in Gaza has depressed enthusiasm among Democrats, too.

Mr. Biden, however, may also be hampered by the very nature of his major legislation, which is meant to achieve transformational and long-term goals like rebuilding the nation’s infrastructure, combating climate change and reinvigorating manufacturing. Problems of that magnitude cannot be solved instantly — or even before voters go to the polls in November. Without immediate results, ambitious legislation can be harder to market.

Elaine Kamarck, a senior fellow at the Brookings Institution and a former official in the Clinton White House, said Mr. Biden’s approach resembled that of Franklin D. Roosevelt, who enacted programs like Social Security that fundamentally altered the fabric of American life.

“Biden is a different generation in that respect. For him, policy is about legacy, as opposed to ‘What will it do for me tomorrow?’” Ms. Kamarck said. “Now, it certainly does pose political issues because people don’t see the results. But I think most people understand that climate change, you don’t solve it overnight.”

In contrast, Mr. Trump brought about more tangible changes when he was in office, like cutting taxes and reshaping the Supreme Court. Although those measures do not necessarily poll well among the broader electorate, they could allow him to drive turnout among Republicans at a time when Mr. Biden is struggling to energize his own base.

Of course, Mr. Biden’s investments in infrastructure and manufacturing are already creating jobs. And he has championed policies with more immediate effects, too, such as capping insulin prices for older people, forgiving some student loan debt and increasing tax subsidies for Affordable Care Act health insurance.

His campaign message has increasingly focused on expanding many of those initiatives to benefit more Americans. At his State of the Union address, Mr. Biden ran through a list of ways he would use a second term to build on the achievements of his first.

“There’s more to do to make sure you’re feeling the benefits of all we’re doing,” Mr. Biden said, promising, in one example, to broaden a $35 cap on insulin beyond older people.

“Now I want to cap the cost of insulin at $35 a month for every American who needs it — everyone,” he said.

In order to sell his message, the Biden campaign plans to lean on the fund-raising advantage it has built over Mr. Trump’s operation, and contrast his record with Mr. Trump’s. In March, the campaign announced a $30 million advertising blitz in battleground states.

“The way that you sell things during campaigns is you go on TV and you tell people about it,” said Mitch Landrieu, the former New Orleans mayor who served as Mr. Biden’s infrastructure czar and is now a co-chairman of his campaign. “You show stories about the real-life people who you are impacting.”

Mr. Biden has lately displayed a more personal touch in trying to connect with voters and illustrate how his presidency is changing their lives, particularly in battleground states. In Michigan, he showed off his putting skills with a Black pastor and his son. In North Carolina, he sat down with a former school principal who had his student loans forgiven.

“We’re looking for ways to make it bite-sized and memorable and driven through the American people telling their story and what this means to them,” said Ben LaBolt, the White House communications director.

Last month, during a trip to the Philadelphia suburbs, Mr. Biden and the first lady, Jill Biden, visited the home of Jack Cunicelli, whose family’s cafe and grocery businesses stayed afloat through the pandemic thanks to aid from Mr. Biden’s Covid-19 relief packages. At the family’s kitchen table, they shared margherita and spinach-ricotta pizza from one of the Cunicellis’ stores. Dr. Biden went out back to help feed the family chickens. Mr. Biden opened up about the loss of his son Beau Biden.

“It felt like family and it felt so natural and normal and they were so disarming,” Mr. Cunicelli recounted in an interview. “And we just made so many connections.”

“I wish everyone got to have that experience,” he added.

But few voters got an up-close view of the sit-down, which lasted more than an hour. Although Mr. Cunicelli later did interviews with local news outlets and the Biden campaign posted photos and videos of the meeting, no reporters were allowed to accompany the president into the family’s home.

Instead, the Biden campaign has used the visits to reach Americans on social media. For instance, it produced a video of the president’s meeting with the former principal in North Carolina that has been viewed more than two million times on TikTok.

Although some polls and consumer survey sentiments show that Americans are starting to feel better about the economy, Mr. Biden is still finding it tough to break through to voters.

In Milwaukee last month, he visited the site of a $36.6 million road improvement project that will try to repair the destructive legacy of a highway routed through African American neighborhoods in the 1960s. It is scheduled to finish in 2029 — after Mr. Biden would have completed a second term.

A sign at the construction site advertised the president’s role, saying the improvements were being financed by “President Joe Biden’s Inflation Reduction Act.”

“Those are President Biden’s fingerprints all over our city every single day,” Mayor Cavalier Johnson of Milwaukee, a Democrat, said in an interview. “Those are his policies.”

But two weeks later, the sign was nowhere to be seen and several residents said they did not know that Mr. Biden’s legislation had paid for the project.

Carlos Gonzalez-Martinez, a public health worker in the neighborhood, said he was still trying to decide whether to vote for Mr. Biden or Mr. Trump.

Mr. Gonzalez-Martinez, 27, suggested that he was for the moment paying attention to more pressing matters, with the election still months away.

“I’m chilling in my little bubble,” he said. “I’m paying my bills.”

Tom Kertscher and Reid J. Epstein contributed reporting from Milwaukee.