US President Joe Biden announced today he will seek a second term in 2024, plunging at the record age of 80 into a campaign that could set up a rematch against Donald Trump.

He launched his pitch in a video released by his new campaign team, in which he declares it is his job to defend American democracy. Biden said he was still fighting to save American democracy from Republican "extremists."

"When I ran for president four years ago, I said we're in a battle for the soul of America, and we still are," Biden said. "Let's finish this job. I know we can," he added.

Challenges in front of Biden as he seeks a second White House term in 2024:

Biden's Age

Biden's age makes his re-election bid a historic and risky gamble for the Democratic Party, which faces a tough election map to hold the Senate in 2024 and is the minority in the House of Representatives now.

Biden is the oldest person to have occupied the White House and would be 86 at the end of a second four-year term. Sixty-one per cent of registered Democrats in a poll said he was too old to work in government.

Doctors declared Biden, who does not drink alcohol and exercises five times a week, "fit for duty" after an examination in February. The White House says his record shows that he is mentally sharp enough for the rigors of the job.

High Inflation

Even though Biden oversaw the lowest levels of unemployment since 1969, a 40-year high in inflation has marred his economic record.

Data showed inflation slowed for a ninth straight month in March to 5.0 percent, income was rising and demand for workers remains strong, with unemployment at just 3.5 percent.

The White House says massive federal investments on infrastructure, climate change and high-tech sectors like semiconductor manufacturing has already ignited an economic rebirth.

But the recession and renewed inflation remain real threats.

US Alliances

"America is back," the Biden administration told the world on day one.

The pledge was to restore alliances strained by Trump's unilateralism. Biden made a quick start, with a focus on face-to-face diplomacy and emphasizing US commitment to NATO and key Asian allies South Korea, Japan and Australia.

He fulfilled a pledge to end the 20-year US war in Afghanistan, but the humiliating exit and Taliban triumph hurt the administration's standing at home and abroad.

There was also a diplomatic hiccup when Australia abruptly scrapped a deal for French submarines in favour of a US nuclear-powered version, prompting Paris briefly to recall its ambassador to Washington.

Biden, however, has received plaudits for his handling of the crisis in Ukraine and for uniting NATO.

Relations with rival superpower China are as rocky as they were under Trump but Biden is trying to walk a diplomatic high wire that he describes as "competition, not conflict."

Guns

An executive order sought to curb untraceable "ghost guns" and Congress enacted a bipartisan law restricting gun access to people deemed dangerous. However, Biden's plea to ban so-called assault weapons often used in mass shootings has gone nowhere.

Immigration

Biden has also struggled on the issue of illegal immigration.

He stopped the Trump project to build a wall on the Mexico border but with Congress unable to agree on legislative changes, he is mostly powerless to reform what he says is a "broken" system.

A new scheme to force asylum seekers to apply in US embassies in their own countries appears to be tamping down illegal border crossings but is controversial among liberal voters.

Low Approval Ratings

Biden's approval ratings have not topped 50 per cent for more than a year and a half.

However, he has consistently over-delivered when it matters. Supporters say the Democratic Party's surprisingly strong performance in the 2022 midterm congressional elections validated the Biden brand.

And while Biden may seem bland in comparison to Trump, he is banking on his moderate, old-fashioned image being the secret weapon needed in an increasingly extreme era.

Biden beat Trump in 2020 by winning the Electoral College 306 to 232. He won the swing states of Pennsylvania and Georgia, and he bested Trump by more than 7 million votes nationally, capturing 51.3 per cent of the popular vote to the Republican's 46.8 per cent.