President Joe Biden's conduct behind closed doors, in the Oval Office, on Air Force One and in meetings around the world is described in the same dual way by those who regularly see him in action.
He is often sharp and focused. But he also has moments, particularly later in the evening, when his thoughts seem jumbled and he trails off mid-sentence or seems confused.
Sometimes he doesn't grasp the finer points of policy details.
He occasionally forgets people's names, stares blankly and moves slowly around the room.
Biden's occasional struggles with focus may not be unusual for someone his age.
But at 81 years old and seeking another four years in the White House, the moments when he's off his game have taken on a fresh resonance following his disastrous debate performance against Republican Donald Trump.
The president appeared pale, gave nonsensical answers, stared blankly and lost his train of thought.
The June 27 faceoff alarmed Democrats and his financial backers, in part, because Biden seemed so much worse than during the almost routine moments when he's less sharp.
And that has raised questions about whether he's up for a campaign that's only going to get nastier and whether he can effectively govern for another four years if he wins.
"We understand the concerns. We get it," White House press secretary Karine Jean-Pierre said this week.
But she insisted Biden has no intention of stepping away from the campaign.
"The president is clear-eyed and he is staying in the race," she said.
But there have been other notable signs in recent weeks, from Biden's constrained itinerary during a recent visit to France to his flat demeanor during a big-dollar Hollywood fundraiser with top stars.
This story is based on interviews with two dozen people who have spent time with the president privately, some of whom were granted anonymity to discuss interactions that were not intended to be public.
How he is in private is how he often is in public — uneven
The way Biden acts in private, according to regular observers, often tracks how he comes off publicly.
In both settings, he can be commanding one day and halting another.
A day after his debate blunder, Biden's voice at a North Carolina rally was forceful, his eyes alert, his delivery confident.
As he spoke, cheers filled the room.
"I give you my word as a Biden. I would not be running again if I didn't believe with all my heart and soul I can do this job," he told supporters.
"Because, quite frankly, the stakes are too high."
But sometimes, Biden speaks so softly that it is difficult to make out his words even with a microphone.
He'll stop mid-sentence and trail off during speeches.
At other times he runs the room, leading the audience, joking and shaking hands with thrilled supporters, in clear command of the moment.
His gait is often stiff, but sometimes he jogs.
His State of the Union speech earlier this year was widely seen as a confident and fiery speech that showed he was ready to take on Trump.
Through it all, public concern about Biden's fitness for another four years has been persistent.
In an August 2023 poll from The Associated Press-NORC Center for Public Affairs Research, fully 77 per cent of US adults said Biden was too old to be effective for four more years.
Not only did 89 per cent of Republicans say that, but so did 69 per cent of Democrats.
Missed opportunities to manage the issue
One person who spends time with Biden regularly said there have been visible signs of his aging over the past year that the president's team has failed to fully address.
The debate performance accelerated concerns about what was already a slow-moving problem, even if Biden has offered assurances that he can still effectively govern.
Biden's advisers have long been aggressively dismissive of questions about his age.
But now they're acknowledging that Biden's slowdown is undeniable.
The debate has forced the president to more frontally acknowledge the limitations of his age, when before he largely made light of it.
But they've taken only largely cosmetic steps to minimize its prominence in the public eye.
They've reduced his use of a long staircase to board Air Force One in favour of a shorter one, and aides often accompany him when he walks in public to make his stiff gait less noticeable.
While his schedule remains busy, aides have built-in recovery stretches — long weekends or extended stays in Delaware at his Wilmington and Rehoboth Beach homes or at Camp David, the presidential retreat in Maryland — to rest up after a gruelling period of travel.
Three French officials who helped organise Biden's visit to France earlier this month said their US counterparts' reactions to options offered for a state visit in Paris and D-Day commemorations in Normandy made them think the president's health must be fragile.
They were told the US president needed some time to rest and they felt Biden's entourage was very protective of him.
Biden's public interactions — with journalists especially — have been greatly limited under a mandate led by one of his top advisers, Anita Dunn.
Even during major events with Democrats or other supporters, the White House sometimes limits how much time Biden spends with the audience, two people said.
At best, it is a protective reflex meant to shield their longtime boss — many at the White House have been with Biden for decades.
But it also can look like an effort to hide something.
A shift in strategy to get Biden out there more
That strategy is shifting in the aftermath of the debate flop.
After internal discussion within the campaign, the White House on Tuesday announced a public blitz: Biden will sit for an interview Friday with ABC's George Stephanopoulos.
The president added a trip to Wisconsin on Friday, and will head to Philadelphia on Sunday.
And he will hold a press conference during the NATO summit in Washington next week.
Biden's allies worry that the next inevitable misstep — even if it's not of the magnitude of his debate disaster — will resurrect voter concerns about the president's fitness for office.
That no matter how hard he tries, Biden may never be able to fully get past it.
A growing body of misleading online videos isn't helping matters.
In one clip, Biden stands very still during a Juneteenth musical performance at the White House, leading to talk he had "frozen."
But Philonise Floyd, George Floyd's brother, was standing next to the president for the performance and disputed the tenor of the clip.
"Joe was just standing there having fun," he told the AP.
Floyd put his arm around Biden during the performance and said the two chatted a bit before the music started and had a great conversation.
One clip, from France, made it seem like he tried to sit down when there wasn't a chair, but there was.
In another widely circulated clip, Biden appears to wander off on a hilltop golf course outside Bari, Italy, during the Group of Seven summit earlier this month, his back turned to leaders who had begun to gather for a group photo.
In reality, he'd turned around to talk to skydivers who had landed behind the leaders, giving them a thumbs up and praising their feats.
The entire scene was chaotic, with skydivers landing all around the leaders and hundreds of staff members standing on the other side of a rope.
Gruelling foreign trips
Those foreign trips can be gruelling, even for the youngest and healthiest of leaders.
And Biden did back-to-back trips in quick succession, first to France and then the G7 visit to Italy.
French officials involved in organising the first trip said his schedule appeared lighter compared with most world leaders' state visits to the country.
After the G7, where Biden appeared pale and his movements slow, he flew across nine time zones to Los Angeles for a glitzy Hollywood fundraiser.
One person who spoke with Biden at the event was struck by how tired the president had seemed during backstage conversations, and grew more concerned when Biden seemed unable to turn it on for his 30-minute onstage conversation with late-night talk show host Jimmy Kimmel and former President Barack Obama.
The same person said that during a fundraiser in March, the president came off as vibrant and engaging and displayed the kind of charm that the person was accustomed to seeing over years of interactions.
During his debate prep sessions at Camp David, Biden seemed to be doing well — ready to take on Trump. So his actual performance came as a shock even to those who were working with him, two of the people said.
At a fundraiser this week, Biden offered up that he had still been recovering from the grueling travel 12 days earlier.
"I wasn't very smart. I decided to travel around the world a couple of times," Biden said.
The president added that he "didn't listen to my staff" about travel and joked that he "fell asleep on stage" during the debate.
How Biden is on the job
Many in the White House say the president is in command across both domestic issues and critical foreign policy problems, like the war in Ukraine and the Israel-Hamas conflict.
"I have been with the president a number of times over the last 3 1/2 years on some of the most consequential kind of life, death or peace-type decisions, and also very high-stakes engagements with senior leaders," said Brett McGurk, a senior National Security Council official who coordinates the Middle East and North Africa.
McGurk has worked for both Republican and Democratic administrations.
"And what I have seen time and again — repeatedly and consistently — from the first week of the administration until now — is a president who prepares for those engagements, who has very detailed and comprehensive briefs for those engagements, and then does the engagement, and then has very active follow-up."
One senior administration official described tense moments with Biden inside the Situation Room, including one on April 13, where over four intense hours Biden and others worked through reports of an imminent attack by Iran on Israel.
Biden gamed out how to respond, and led complicated discussions with Prime Minister Benjamin Netanyahu and other G7 leaders, working to ensure there was no broader regional conflict.
Domestic policy adviser Neera Tanden said in recent weeks she has been in private meetings with Biden and in larger group settings on major policy issues, including potential citizenship for more migrants, new healthcare data and the FBI's crime statistics.
She said the president was engaged, thorough and fully in command of the policies.
"I take him very complicated issues, and he handles them," she said.
"He understands how programs are complicated and interconnected, and he can connect things to experiences he's had a long time ago, or experiences they've had a few months ago."
New Jersey governor Phil Murphy described a weekend fundraiser that raised millions for Biden.
It included a sit-down meal where the president, first lady and governor chatted with supporters and took a round of unscripted questions.
"He weighed in on all of the above, substantively — I'll give you a smattering, universal pre-K, free community college, the Ukraine war, Middle East war, Federal Reserve, general economy, wage growth, job growth."
Unsatisfied with the explanations
Democrats, so far, have been largely unsatisfied with the explanations for Biden's debate performance from White House staff, his campaign and the president himself.
And there is a deeper frustration among some who feel like the president should have handled this much sooner, and he has put them in a difficult position by staying in the race.
Biden could decide to drop out of the race, but he can't be removed. So far only two active members of Congress have called for him to step aside, but there is growing anxiety on Capitol Hill about his ability to do the job and many are anxiously awaiting post-debate polling and waiting to see how he handles his Friday interview on ABC.
Another problem for Democrats: With the focus so squarely on Biden, there has been less attention paid to Trump, whose debate performance was riddled with falsehoods about the January 6, 2021, Capitol riot, Democrats' views on abortion rights and his own revisionist comments about his response on a 2017 neo-Nazi rally.
One Democratic ally expressed frustration that Biden's family members have not called on him to step aside for the sake of the top priority: Keeping Trump out of the White House. Instead, they're encouraging him to stay in the race.
Only Biden's doctors can really answer
Really, only Biden's personal physician can answer questions about the president's cognitive fitness — and given the level of public concern, he should do so, said well-known ageing researcher S. Jay Olshansky of the University of Illinois at Chicago.
One bad appearance on TV isn't enough to assess anyone's cognitive ability, Olshansky stressed, "even for those of us that study aging for a living".
Without more insight, there's no way to know if the jet lag Biden has cited, or other factors, explain the performance, he said.
"I certainly know how it looks, and it did not look good. But can we attribute it to cognitive decline? Look, an hour after he was participating in that debate, and the day after, he looked back to his old self," Olshansky said.
"But the fact that we don't know for sure is the problem."
"The only person that's ever examined the president from a medical perspective is his personal physician," he added.
"The important message is that we don't know and we haven't heard from his physician. And until those issues are resolved it just seems to be a festering wound."
Biden's physician, Dr Kevin O'Connor, deemed the president fit for duty after a February checkup that included a neurologic assessment.
White House officials at the time said Biden wasn't given a specific cognitive test because O'Connor and the neurologist decided he didn't need one.
"His doctor's a very good one and he doesn't do unnecessary tests," Olshansky said.
"So when he made the decision not to do it, that told us a compelling story about what he saw and what he didn't see — which is no evidence of cognitive decline" at that time.
