Future Democratic presidential prospects are taking steps to strengthen their national profiles as they fan out across America to help President Joe Biden’s re-election campaign.

The 80-year-old US leader could face a tough rematch next autumn with Donald Trump, who he defeated in 2020.

Mr Biden is issuing increasingly dire warnings about the implications of a Trump win for American democracy, delivering a passionate speech on the issue on Thursday in Arizona.

“We should all remember, democracies don’t have to die at the end of a rifle,” Mr Biden said.

“They can die when people are silent, when they fail to stand up or condemn threats to democracy, when people are willing to give away that which is most precious to them because they feel frustrated, disillusioned, tired, alienated.”

However, Mr Biden is facing questions about his political strength and his age. Privately, those close to a number of ambitious Democrats indicate that their jockeying is much more about positioning themselves for the 2028 presidential contest than making a move for 2024.

Mr Biden, who turns 81 in November, would be 86 at the end of a second term should he be successful in 2024.

The new crop of rising stars have all endorsed Mr Biden. But in building their national profiles, they are not only getting into position for future presidential runs but also giving the party something of an insurance policy in case they are suddenly needed, due to unforeseen circumstances, next year.

Among the frontrunners, Pennsylvania’s Democratic governor Josh Shapiro is set to address presidential primary voters in New Hampshire on Saturday.

Michigan governor Gretchen Whitmer is working to strengthen Democratic parties across the US Midwest.

And California governor Gavin Newsom was the Biden campaign’s surrogate during the second Republican presidential debate this week – and he has agreed to a one-on-one debate against a top Republican presidential contender.

Mr Shapiro said in an interview: “We’ve got a lot of talent in our party, and that talent is unified behind the re-election of President Joe Biden.

“And I’m excited for the next couple of years, and for the future of our party. I think we’re in a strong position.”

Mr Biden announced his re-election bid in April and his allies insist that only an unforeseen physical challenge could force him from the race. He is taking all the usual steps to support a growing re-election effort, including adding staff to his Delaware-based campaign that now employs about 50 people.

The campaign is also launching a spree of advertising with the Democratic National Committee. The push includes a months-long, 25 million dollar (£20.5 million) digital and television blitz focused on issues ranging from the administration’s economic policies to efforts to protect abortion rights.

The ads are airing in battleground states such as Arizona, Georgia and Pennsylvania.

As well as warning over the perils of a Trump victory, the administration has a record they are eager to run on, including signing into law major investments in health care, climate change, pandemic relief and the economy.

US inflation is ticking down, while the unemployment rate and economic growth remain strong. The Republicans’ efforts to roll back abortion rights have also repelled many voters, even in Republican-leaning states.

For now, such efforts have not lifted Mr Biden’s weak approval ratings or neutralised the political fallout from an evolving criminal case against his son.

And it has done little to address what may be the President’s most potent vulnerability: his age. About three-quarters of Americans – 77% – said Mr Biden is too old to be effective for another four years, according to a poll released last month from The Associated Press-NORC Centre for Public Affairs Research. That view was held by 89% of Republicans and, notably, 69% of Democrats.

Donald Trump is 77.

California Democratic representative Ro Khanna is a progressive leader who has already spoken to New Hampshire’s presidential primary voters three times this year. In an interview, he warned Democrats against promoting a message of “triumphalism” in 2024 by simply touting Mr Biden’s accomplishments.

“The American dream has slipped away for too many Americans. The working class has been shafted and there’s still a lot of anger out there,” Mr Khanna said. “We’re trying to turn the ship, but it’s gonna require bolder and more focused action to help the working class.”

The conversation among Democrats is blunter in private. On the sidelines of a recent meeting of the National Governors Association in New Hampshire, several senior Democratic aides were overheard by a reporter discussing the type of candidate who could stand in for Mr Biden if needed.

And at least one major political group aligned with the Democrats is in the process of formulating a contingency plan in the unlikely event that Mr Biden is not on the ballot, according to one top official within that group. The group is also developing options for the possibility that Mr Trump, the overwhelming front-runner, is not the Republican nominee.

The Biden re-election campaign said any group questioning the president being on the 2024 ballot is not aligned with anyone of consequence in the Democratic Party.

There is also a lack of confidence among some donors and party officials in vice president Kamala Harris as a Biden successor. She has struggled with weak ratings of her own.