WASHINGTON – There was the time last winter when US President Joe Biden was awakened at 3am while on a trip to Asia and told that a missile had struck Poland, touching off a panic that Russia might have expanded the war in Ukraine to a Nato ally.

Within hours in the middle of the night, Mr Biden consulted his top advisers, called the President of Poland and the Nato Secretary-General, and gathered fellow world leaders to deal with the crisis.

And then there was the time a few weeks ago when Mr Biden was hosting children for Take Your Child To Work Day and became mixed up as he tried to list his grandchildren. “So, let me see. I got one in New York, two in Philadelphia – or is it three? No, three, because I got one granddaughter who is – I don’t know. You’re confusing me.”

He also drew a blank when asked the last country he had visited and the name of a favourite movie.

The two Joe Bidens co-exist in the same octogenarian president: sharp and wise at critical moments, the product of decades of seasoning, able to rise to the occasion even in the dead of night to confront a dangerous world. Yet a little slower, a little softer, a little harder of hearing, a little more tentative in his walk, a little more prone to occasional lapses of memory in ways that feel familiar to anyone who has reached their ninth decade or has a parent who has.

The complicated reality of America’s oldest president was encapsulated on Thursday as Congress approved a bipartisan deal he brokered to avoid a national default. Even Speaker Kevin McCarthy testified that Mr Biden had been “very professional, very smart, very tough” during their talks.

Yet, just before the voting got under way, Mr Biden tripped over a sandbag at the Air Force Academy commencement, plunging to the ground. The video went viral, his supporters cringed and his critics pounced.

Anyone can trip at any age, but for an 80-year-old president, it inevitably raises unwelcome questions. If it were anyone else, the signs of age might not be notable. But Mr Biden is the chief executive of the world’s most powerful nation and has just embarked on a campaign asking voters to keep him in the White House until age 86, drawing more attention to an issue that polls show troubles most Americans and is the source of enormous anxiety among party leaders.

The portrait that emerges from months of interviews with dozens of current and former officials and others who have spent time with him lies somewhere between the partisan cartoon of an addled and easily manipulated fogy promoted by Republicans and the image spread by his staff of a president in aviator shades commanding the world stage and governing with vigor.

It is one of a man who has slowed with age in ways that are more pronounced than just the graying hair common to most recent presidents during their time in office. Mr Biden sometimes mangles his words and looks older than he used to because of his stiff gait and thinning voice.

Yet, people who deal with him regularly, including some of his adversaries, say he remains sharp and commanding in private meetings. Diplomats share stories of trips to places such as Ukraine, Japan, Egypt, Cambodia and Indonesia in which he often outlasts younger colleagues. Democratic lawmakers point to a long list of accomplishments as proof that he still gets the job done.

His verbal miscues are nothing new, friends note; he has struggled throughout his life with a stutter and was a “gaffe machine”, to use his own term, long before he entered Social Security years. Advisers said his judgment is as good as ever. So many of them use the phrase “sharp as a tack” to describe him that it has become something of a mantra.

Mr Biden says age is a legitimate issue but maintains that his longevity is an asset, not a liability. “You say I’m ancient?” he said at the White House Correspondents’ Association dinner in April. “I say I’m wise.”

Polls indicate Mr Biden’s age is a top concern of Americans, including Democrats. During a recent New York Times focus group, several voters who supported Mr Biden in 2020 expressed worry, with one saying: “I’ve just seen the blank stare at times, when he’s either giving a speech or addressing a crowd. It seems like he loses his train of thought.”

In private, officials acknowledge that they make what they consider reasonable accommodations not to physically tax an ageing president. His staff schedules most of his public appearances between noon and 4pm and leave him alone on weekends as much as possible.

A study of Mr Biden’s schedule based on data compiled by Axios and expanded by the Times found that Mr Biden has a similar morning cadence as the president he served, Mr Barack Obama. Neither had many public events before 10am, just 4 per cent in Mr Obama’s last year in office and 5 per cent in Mr Biden’s first 2½ years. But the real difference came in the evening. Mr Obama was twice as likely to do public events after 6pm compared with Mr Biden, 17 per cent to 9 per cent.

Aides limit exposing Mr Biden to news media interviews when he could make a politically damaging mistake. He has given just one-fourth of the interviews Mr Donald Trump did in the same time period and one-fifth of Mr Obama’s interviews – and none at all to reporters from a major newspaper.

Mr Biden has not given an interview to the news department of the Times, unlike every president since at least Franklin D. Roosevelt, other than Dwight D. Eisenhower. And in the past 100 years, only presidents Ronald Reagan and Richard Nixon have subjected themselves to as few news conferences.

Like many his age, Mr Biden repeats phrases and retells the same hoary, often fact-challenged stories again and again. He can be quirky; when children visit, he may randomly pull a book of William Butler Yeats off his desk and start reading Irish poetry to them.

At the same time, he is trim and fit, exercises five days a week and does not drink. He has at times exhibited striking stamina, such as when he flew to Poland, boarded a nine-hour train ride to make a secret visit to Ukraine’s capital Kyiv, spent hours on the ground, then endured another nine-hour train ride and a flight to Warsaw, Poland.

A study of his schedule by Mr Biden’s aides shows that he has travelled slightly more in the first few months of his third year in office than Mr Obama did in his.

“Does he ramble? Yes, he does,” said New Jersey Governor Phil Murphy, a Democrat who categorically rejects the idea that Mr Biden is too old to be president.

“Has he always rambled? Yes, he has. Public and private. He’s the same guy. He’s literally – I’m not saying this lightly – I don’t know anyone else in my life who is so much the same guy privately as he is publicly.”

The question of Mr Biden’s age does not come in isolation, of course. Mr Trump, his likeliest Republican challenger, is just four years younger and was the oldest president in history until Mr Biden succeeded him. If Mr Trump were to win next year, he would be 82 at the end of his term, older than Mr Biden will be at the end of this one.

While in office, Mr Trump generated concerns about his mental acuity and physical condition. He did not exercise, his diet leaned heavily on cheeseburgers and steak, and he officially tipped the scales at 110kg, a weight formally deemed obese for his height.

After complaining that he was overscheduled with morning meetings, Mr Trump stopped showing up at the Oval Office until 11am or 11.30am each day, staying in the residence to watch television, make phone calls or send out incendiary tweets. During an appearance at the US Military Academy at West Point, he had trouble lifting a glass of water and seemed to have trouble making his way down a modest ramp.

Mr Biden lately has turned to self-deprecating humour to defuse the issue, taking a cue from Mr Reagan, who won re-election in 1984 at age 73 in part with a well-timed debate quip about not exploiting “my opponent’s youth and inexperience”.

At the correspondents’ dinner, Mr Biden assured the audience that he supported the First Amendment, and “not just because my good friend Jimmy Madison wrote it”.

During the Take Your Child To Work Day event, he looked back on “when I was younger, 120 years ago”.

At the Air Force Academy a few days ago, Mr Biden joked that “when I was graduating from high school 300 years ago, I applied to the Naval Academy”.

After tripping on the sandbag, he sought to laugh that off too. “I got sandbagged,” he said. NYTIMES