A Bloomberg News/Morning Consult survey this month found voters in seven swing states more likely to associate old age with Biden than any other topic. In an open-ended question asking what they had heard about the candidates lately, hundreds of respondents cited Biden’s age. Fewer than a dozen did the same for Trump.

Those perceptions have been fuelled by high-profile moments including his fall at a US Air Force Academy graduation, staircase stumbles boarding Air Force One, the revelation he was using a medical device to aid his breathing during sleep, and a series of verbal gaffes.

Taken together, they have fanned uneasiness among Democrats that the man who has cast himself as the bulwark against Trump’s return is just one illness or injury from plunging his campaign – and the nation – into calamity.

White House aides have created a safety net of small accommodations, including regularly using a lower set of stairs for boarding Air Force One, to avoid giving fodder to opponents or the news media.

Secret Service agents and staff are careful in cramped backstage settings, using flashlights and verbal warnings to guide the president’s path, according to a person familiar with the matter.

The president also interacts less frequently with the White House press corps, holding far fewer formal press conferences or off-the record sessions on Air Force One and only sitting for a single interview with a daily newsprint journalist.

Aides say his press strategy is deliberate, reflecting the changing media landscape. And while Biden’s wariness of the press is a stark departure from Trump – and his own time as vice-president – those travelling with the president maintain his gift for gab hasn’t diminished, and that he often spends long flights peppering sleepy staffers with questions.

Biden allies also call the focus on the president’s age and health unfair, considering his chief rival, 77-year-old Trump, is medically obese and disdainful of exercise beyond the golf course. And while Trump regularly mocks Biden’s acuity on the campaign trail, he’s prone to slips of his own.

In recent weeks, Trump has incorrectly identified which city he is in, implored his supporters not to vote, and erroneously suggested he was running against or had run against former president Barack Obama. The miscues have become fodder for rivals including Florida Governor Ron DeSantis, who has suggested on the campaign trail that Trump has lost a step.

Biden himself has taken to handling the topic of his age with a light touch. He makes regular quips suggesting he’s been in Washington since the days of the Founding Fathers. When an attendee at a union event earlier this month fell off a riser – causing a loud noise to interrupt the event – Biden seized the moment for laughs.

The president’s doctors have also said that certain noticeable traits – like his shuffled gait following a foot injury, or the re-emergence of his stutter when tired – are unrelated to questions of acuity.

Some of Biden’s verbal stumbles during speeches appear to stem from his decision – like Trump – not to wear glasses in public, leaving him squinting as he reads a teleprompter.

And while age and injury have heightened his golf handicap, people who interact with the president say he’s dedicated to his workout routines and diligently follows a weights-and-treadmill programme prescribed by the White House doctor and written out on a notecard.

He bikes, often at considerable speed, while holidaying in Rehoboth Beach in Delaware and at Camp David, the presidential retreat in Maryland.

Aides have developed a playbook for swatting down age questions. They offer ways his longevity has been an asset, such as in negotiations on Capitol Hill where he marshaled decades of institutional knowledge.

“He has used his deep experience to deliver unprecedented benefits,” White House spokesman Andrew Bates said in a statement, adding that Republican Party criticisms of the president’s age “failed in 2020, 2022, and 2023”.

Aides also highlight displays of stamina, such as Biden’s trips to Ukraine – the first by a modern American president to a war zone not under control of US forces – and to Israel in the days following the October 7 attack by Hamas.

“There’s nothing about his physical health, his acuity, any aspect of his performance that gives me an iota of concern in this space – because I interact with him regularly,” said Jared Bernstein, chairman of the White House Council of Economic Advisers.

Still, voters’ concerns remain. Now, the rituals of the campaign trail, including schmoozing with donors at fundraising events and engaging in off-the-cuff chatter with voters, provide fresh opportunities to beat back perceptions of frailty – or feed right into them.

Rope lines and big-city fundraisers haven’t always shown the president in his best light. Earlier this year, when White House staffers’ kids visited for Take Your Child to Work Day, Biden took part in an impromptu question-and-answer session.

During his exchanges with the children, he forgot that he had just visited Ireland, and struggled – after saying they spoke every day – to recall where his grandchildren lived.

He’s mixed up the names of world leaders, often conflating China’s Xi Jinping with India’s Narendra Modi. At the Asia-Pacific Economic Cooperation summit last week in San Francisco, Biden said he forgot the name of a reporter he intended to call on.

Biden can ill afford those kinds of moments when 58 per cent of voters say they have doubts about his fitness for office and 67 per cent said he was too old to be president, according to a Harvard-Harris poll released last month.

Nevertheless, his aides believe they know how to overcome those challenges.

“If you remember our ads in 2020, they had the president in them – they had his voice, they had him showing that he’d just be doing the job,” Jen O’Malley Dillon, who served as Biden’s campaign manager in that election and now as White House deputy chief of staff. “In some ways, that’s the most effective thing for us to do, which is continue to show the president doing the job.”