Time waits for no man, the saying goes - and for 80-year-old Joe Biden, that could be a problem. Can the US president convince voters that his age is not an issue?

Mr Biden announced on Tuesday that he wants to serve another four years in the White House. Americans, according to a recent NBC News poll, aren't so sure.

The survey shows that 70% of Americans - and 51% of Democrats - think he shouldn't seek re-election. And it identifies one major concern for about half of those who want him to stand aside in 2024: his age.

Mr Biden is already the oldest president in US history. If he were to win re-election, he would be inaugurated at age 82 and finish his second four-year term at 86. According to US government actuarial tables, the average life expectancy for an 82-year-old man is 6.77 years, with an 8% chance of death within the next 12 months.

The video, which broadly outlines his plan to protect "personal freedoms" and warns against threats posed by his Republican opponents, does not tackle the age issue head on. Instead, it intersperses cuts of an animated president - jogging here, looking engaged there - set to swelling instrumental music.

The video also repeatedly highlights Vice-President Kamala Harris, who would take over the presidency if Mr Biden were incapacitated. At 58, the Biden team may hope her presence injects a bit of life and energy into the campaign. Then Vice-President Biden, it should be noted, was missing from Barack Obama's 2012 re-election video.

The video is not going to be enough, according to veteran political consultant Bob Shrum, director of the Center for the Political Future and a former senior adviser to the presidential campaigns of Democrats Al Gore and John Kerry.

"You answer age questions by running a vigorous campaign," Mr Shrum said. "You don't answer it by talking about it."

He added that the age issue will only become a problem if Mr Biden has a "serious" mistake or stumble on the campaign trail. And if that's the case, the Republicans - who are already trying to amplify every Biden gaffe - will be ready to make the case that Mr Biden is no longer fit for the presidency.

Last year, 54 Republicans in the House of Representatives signed a letter to the White House expressing "concern" about Mr Biden's cognitive state and demanding that Mr Biden take a dementia test.

The letter went on to list a number of Biden missteps and misstatements during his presidency.

"These recent gaffes are not isolated incidents, as they are part of a larger history of your actions which exemplify cognitive decline," the letter read.

These kind of pointed "concerns" have been echoed by Donald Trump, who is currently the leading contender for the Republican 2024 presidential nomination. At political rallies in the run-up to the midterm congressional elections last year, Mr Trump frequently played a video for the crowd of Mr Biden's various gaffes and stumbles.

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"Voters say, look, they're both old," Mr Messina told the BBC Americast podcast. "Tell me who's going to make my life better."

"Democrats do one thing every night," he continued. "We sit down, and we get on our knees, and we pray to God that Donald Trump is the Republican nominee for president."

Mr Biden also faced questions about his age four years ago, although the nature of the presidential race in the midst of the Covid-19 pandemic helped insulate the candidate from some of the exposure that comes with a national primary and general election campaign. And in the end, the age issue was a non-factor in Mr Biden's victory over Mr Trump.

This time around, Mr Biden will enjoy the benefits of campaigning as the incumbent president. That includes travel on Air Force One and attending political events that are meticulously planned not just by professional campaign staff but also by the president's extensive security detail.

It is a very different type of experience to what non-incumbent candidates must face. His rivals will have to battle through primaries in the snows of New Hampshire and Iowa, often running on shoestring budgets and competing in a crowded field which can take more than a year to vanquish.

That will give Mr Biden the luxury of a running start against his Republican opponent. The period of frenzied active campaigning he will have to endure can be measured in weeks and months in the second half of 2024.

And if there were a bit of silver lining to the NBC poll showing a national reluctance to embrace Mr Biden's re-election bid, it's that if Mr Biden does run again, 88% of Democrat said they would definitely or probably support their candidate.

"Biden is always underestimated," Mr Shrum said. "Biden was underestimated in 2020. People wrote him off after the first couple of primaries, and then he went on to win the primaries by a landslide."