U.S. President Joe Biden on Tuesday formally announced his bid for a second term, calling on voters to keep him in office to do more for the defense of democracy and framing the 2024 presidential election as a choice between "more freedom or less freedom."

"When I ran for president four years ago, I said we were in a battle for the soul of America. And we still are," he said in a campaign-style pre-recorded video, which opens with a scene from the Jan. 6, 2021, attack on the U.S. Capitol by supporters of former President Donald Trump.

Biden's candidacy for the election was declared on the fourth anniversary of his entry into the 2020 race, while concerns about his age persist among many voters. At 80, he is already the oldest president in U.S. history, and he would be 86 at the end of a potential second four-year term.

"The question we are facing is whether in the years ahead we have more freedom or less freedom. More rights or fewer. I know what I want the answer to be and I think you do, too," the president said. "This is not a time to be complacent. That's why I'm running for re-election."

U.S. President Joe Biden speaks at the North America's Building Trades Union National Legislative Conference at the Washington Hilton in Washington on April 25, 2023. (AP/Kyodo)

Having finally tossed his hat in the ring, Biden will kick off fundraising for his campaign. The announcement, which came as no surprise, could eventually lead to a rerun of the 2020 contest between him and Trump, a matchup that polling has shown much of the U.S. electorate would rather not see.

The Democratic president previously signaled his intention to seek re-election, while First Lady Jill Biden also said in February that her husband would run for a second term.

In the lead-up to Tuesday's announcement, Biden underscored his administration's achievements, ranging from the country's decades-low unemployment rate, COVID-19 recovery and a domestic manufacturing revival to incentives for low-carbon products and stricter gun control measures.

A few hours after the launch, Biden gave a speech in Washington before an audience of trade union members who chanted "four more years." He repeated the list of accomplishments since taking office in January 2021, and said he looks at the world through the eyes of "working people" rather than those of Wall Street.

"We're creating jobs again. Manufacturing has come alive again. People can afford a decent health care. Towns that have been forgotten and left behind for dead are coming alive again because of you all and what we're doing," he said. "Now we've just got to keep it going."

Vice President Kamala Harris, who is featured prominently in the three-minute video, entitled "Freedom," said she will be Biden's running mate in the next election, calling it a "pivotal moment in our history."

Biden's team said the 2024 campaign will be managed by Julie Rodriguez, a senior White House adviser also involved in his previous run.

No serious rival for the party's nomination has emerged so far, although the incumbent's popularity has been tepid, even among Democrats.

An NBC News poll released Sunday showed only 26 percent of voters in the United States think Biden should run for a second term, while 70 percent believe he should not, with concerns over his age cited as a major reason.

The same national survey found that Trump, 76, continues to be far ahead of all of his Republican competitors, despite the recent indictment against him over a hush money payment to a porn star and other investigations into his past conduct.

In the video, which was released early Tuesday morning and also included images of abortion rights activists protesting at the U.S. Supreme Court, Biden warned that fundamental rights guaranteed in the United States are threatened by Trump's allies.

"Every generation of Americans has faced a moment when they have to defend democracy. Stand up for our personal freedom. Stand up for the right to vote and our civil rights. And this is our moment," he said. "Let's finish this job. I know we can."

Trump, meanwhile, intensified his attacks on Biden, saying in a statement that due to his "socialist spending calamity, American families are being decimated by the worst inflation in half a century."

Until now, the only Democrats to launch bids for the 2024 nomination had been Marianne Williamson, a 70-year-old self-help author, and Robert F. Kennedy Jr., a 69-year-old scion of one of the country's best-known political families who has become famous for his anti-vaccine views.

Trump's rivals for the Republican nomination include Nikki Haley, a 51-year-old former ambassador to the United Nations, and Ron DeSantis, 44, who currently serves as the governor of Florida and is expected to announce his candidacy soon.