WASHINGTON -- U.S. President Joe Biden on Tuesday formally announced that he is running for re-election in 2024, asking voters to give him more time to "finish this job" and extend the run of America's oldest president for another four years.

Biden, who would be 86 at the end of a second term, is betting his first-term legislative achievements and more than 50 years of experience in Washington will count for more than concerns over his age. He faces a smooth path to winning his party's nomination, with no serious Democratic challengers. But he's still set for a hard-fought struggle to retain the presidency in a bitterly divided nation.

In his first public appearance Tuesday since the announcement, Biden offered a preview of how he plans to navigate the dual roles of president and presidential candidate, using a speech to building trades union members to highlight his accomplishments and undercut his GOP rivals, while showing voters he remained focused on his day job.

Greeted with chants of "Let's Go Joe" from a raucous crowd of building trades union members -- a key base of Democratic support -- Biden showcased the tens of thousands of construction jobs being created since he took office that are supported by legislation he signed into law.

"We -- you and I -- together we're turning things around and we're doing it in a big way," Biden said. "It's time to finish the job. Finish the job."

Biden's campaign announcement, in a three-minute video, comes on the four-year anniversary of when he declared for the White House in 2019, promising to heal the "soul of the nation" amid the turbulent presidency of Donald Trump -- a goal that has remained elusive.

"I said we are in a battle for the soul of America, and we still are," Biden said. "The question we are facing is whether in the years ahead we have more freedom or less freedom. More rights or fewer."

While the prospect of seeking re-election has been a given for most modern presidents, that's not always been the case for Biden. A notable swath of Democratic voters has indicated they would prefer he not run, in part because of his age. Biden has called those concerns "totally legitimate" but he did not address the issue head-on in his launch video.

Yet few things have unified Democratic voters like the prospect of Trump returning to power. And Biden's political standing within his party stabilized after Democrats notched a stronger-than-expected performance in last year's midterm elections. The president is set to run again on the same themes that buoyed his party last fall, particularly on preserving access to abortion.

"Freedom. Personal freedom is fundamental to who we are as Americans. There's nothing more important. Nothing more sacred," Biden said in the launch video, depicting Republican extremists as trying to roll back access to abortion, cut Social Security, limit voting rights and ban books they disagree with. "Around the country, MAGA extremists are lining up to take those bedrock freedoms away."

As the contours of the campaign begin to take shape, Biden plans to run on his record. He spent his first two years as president combating the coronavirus pandemic and pushing through major bills such as the bipartisan infrastructure package and legislation to promote high-tech manufacturing and climate measures.

The president also has multiple policy goals and unmet promises from his first campaign that he's asking voters to give him another chance to fulfil.

"Let's finish this job. I know we can," Biden said in the video, repeating a mantra he said a dozen times during his State of the Union address in February.

Vice President Kamala Harris, who was featured prominently alongside Biden in the video, held a political rally at Howard University in Washington on Tuesday evening in support of abortion access, kicking off her own efforts to support the re-election effort.

Saying she's "proud to run for re-election with President Joe Biden," Harris added, "Our hard-won freedoms are under attack. And this is a moment for us to stand and fight."

In the video, Biden speaks over brief clips and photographs of key moments in his presidency, snapshots of diverse Americans and flashes of outspoken Republican foes, including Trump, Florida Gov. Ron DeSantis, and Rep. Marjorie Taylor Greene of Georgia. He exhorts supporters that "this is our moment" to "defend democracy. Stand up for our personal freedoms. Stand up for the right to vote and our civil rights."

Biden also plans to point to his work over the past two years shoring up American alliances, leading a global coalition to support Ukraine's defences against Russia's invasion and returning the U.S. to the Paris climate accord. But public support in the U.S. for Ukraine has softened in recent months, and some voters question the tens of billions of dollars in military and economic assistance flowing to Kyiv.

The president also faces lingering criticism over his administration's chaotic 2021 withdrawal from Afghanistan after nearly 20 years of war, which undercut the image of competence he aimed to portray, and he's the target of GOP attacks over his immigration and economic policies.

As a candidate in 2020, Biden pitched voters on his familiarity with the halls of power in Washington and his relationships around the world. But even back then, he was acutely aware of voters' concerns about his age.

"Look, I view myself as a bridge, not as anything else," Biden said in March 2020, as he campaigned in Michigan with younger Democrats, including Harris, Sen. Cory Booker of New Jersey and Michigan Gov. Gretchen Whitmer. "There's an entire generation of leaders you saw stand behind me. They are the future of this country."

Three years later, the president now 80, Biden allies say his time in office has demonstrated that he saw himself as more of a transformational than a transitional leader.

Still, many Democrats would prefer that Biden didn't run again. A recent poll from The Associated Press-NORC Center for Public Affairs Research shows just 47% of Democrats say they want him to seek a second term, up from 37% in February. And Biden's verbal -- and occasional physical -- stumbles have become fodder for critics trying to cast him as unfit for office.

During a routine physical in February, Biden's physician, Dr. Kevin O'Connor, declared him "healthy, vigorous" and "fit" to handle his White House responsibilities.

Hours after Biden's announcement, White House press secretary Karine Jean-Pierre initially refused to say whether the president planned to serve all eight years if elected to a second term. She later clarified by tweet that "I wanted to be sure that I didn't go into 2024 more than is appropriate under the law. But I can confirm that if re-elected, @POTUS would serve all 8 years."

Aides acknowledge that while some in his party might prefer an alternative to Biden, there is anything but consensus within their diverse coalition on who that might be. And they insist that when Biden is compared with whomever the GOP nominates, Democrats and independents will rally around Biden.

For now, the 76-year-old Trump is the favourite to emerge as the Republican nominee, creating the potential of a historic sequel to the bitterly fought 2020 campaign. But Trump faces significant hurdles of his own, including the designation of being the first former president to face criminal charges. The remaining GOP field is volatile, with DeSantis emerging as an early alternative to Trump. DeSantis' stature is also in question, however, amid questions about his readiness to campaign outside of his increasingly Republican-leaning state.

To prevail again, Biden will need the alliance of young voters and Black voters -- particularly women -- along with blue-collar Midwesterners, moderates and disaffected Republicans who helped him win in 2020. He'll have to again carry the so-called "blue wall" in the Upper Midwest, while protecting his position in Georgia and Arizona, long-time GOP strongholds he narrowly won last time.

Biden spoke Tuesday with Democratic governors about his re-election plans, while aides and allies briefed key political groups, grassroots organizers and state party officials on strategy, his campaign said. The president was set to huddle later this week in Washington with prominent party donors.

Biden's re-election bid comes as the nation weathers uncertain economic crosscurrents. Inflation is ticking down after hitting the highest rate in a generation, but unemployment is at a 50-year low, and the economy is showing signs of resilience despite Federal Reserve interest rate hikes.

"If voters let Biden `finish the job,' inflation will continue to skyrocket, crime rates will rise, more fentanyl will cross our open borders, children will continue to be left behind, and American families will be worse off," Republican National Committee Chair Ronna McDaniel said in a statement.

Presidents typically try to delay their re-election announcements to maintain the advantages of incumbency and skate above the political fray for as long as possible while their rivals trade jabs. But the leg up offered by being in the White House can be rickety -- three of the last seven presidents have lost re-election, most recently Trump in 2020.

Biden's announcement is roughly consistent with the timeline followed by then-President Barack Obama, who waited until April 2011 to declare for a second term and didn't hold a re-election rally until May 2012. Trump launched his re-election bid on the day he was sworn in in 2017.

On Tuesday, Biden named White House adviser Julie Chavez Rodriguez to serve as campaign manager and Quentin Fulks, who ran Sen. Raphael Warnock's re-election campaign in Georgia last year, to serve as principal deputy campaign manager. The campaign co-chairs will be Reps. Lisa Blunt-Rochester, Jim Clyburn and Veronica Escobar; Sens. Chris Coons and Tammy Duckworth; entertainment mogul and Democratic mega-donor Jeffrey Katzenberg; and Whitmer.

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AP writer Chris Megerian contributed.