"Are you up?" The e-mails arrive late, often after 1am, tapped out on a secure BlackBerry from an e-mail address known only to a few. The weary recipients know that once again, the boss has not yet gone to bed.
The late-night interruptions from US President Barack Obama might be sharply worded questions about memos he has read. Sometimes, they are taunts because the recipient's sports team just lost.
Last month, it was a 12.30am e-mail to deputy national security adviser Ben Rhodes and White House chief of staff Denis McDonough, telling them he had finished reworking a speechwriter's draft of presidential remarks for later that morning. Mr Obama had spent three hours scrawling in longhand on a yellow legal pad an angry condemnation of presidential hopeful Donald Trump's response to the attack in Orlando, Florida, and told his aides they could pick up his rewrite at the White House usher's office when they came in for work.
Mr Obama calls himself a "night guy" and, as president, he has come to consider the long, solitary hours after dark as essential as his time in the Oval Office. Almost every night that he is in the White House, Mr Obama has dinner at 6.30pm with his wife and daughters and then withdraws to the Treaty Room, his private office down the hall from his bedroom on the second floor of the White House residence. There, his closest aides say, he spends four or five hours largely by himself.
He works on speeches. He reads the stack of briefing papers delivered at 8pm by the National Security Council staff secretary. He reads 10 letters from Americans chosen each day by his staff. "How can we allow private citizens to buy automatic weapons? They are weapons of war," Ms Liz O'Connor, a Connecticut middle school teacher, wrote in a letter Mr Obama read on the night of June 13.
The President also watches ESPN, reads novels or plays Words With Friends on his iPad.
Mrs Michelle Obama occasionally pops in, but she goes to bed before the President, who is up so late he barely gets five hours of sleep a night. For Mr Obama, the time alone has become more important.
"Everybody carves out their time to get their thoughts together. There is no doubt that window is his window," said Mr Rahm Emanuel, Mr Obama's first chief of staff. "You can't block out a half-hour and try to do it during the day. It's too much incoming. That's the place where it can all be put aside and you can focus."
Former president George W. Bush, an early riser, was in bed by 10pm, while president Bill Clinton was up late like Mr Obama, but he spent the time in lengthy, freewheeling phone conversations with friends and political allies, forcing aides to scan the White House phone logs in the mornings to keep track of who the president might have called the night before.
"A lot of times, for some of our presidential leaders, the energy they need comes from contact with other people," said historian Doris Kearns Goodwin, who has had dinner with Mr Obama several times in the past 71/2 years. "He seems to be somebody who is at home with himself."
AN INSANE AMOUNT OF PAPER
When Mr Obama first arrived at the White House, his after-dinner routine started around 7.15pm in the game room, on the third floor of the residence. There, on an old Brunswick pool table, Mr Obama and Mr Sam Kass, then the Obama family's personal chef, would spend 45 minutes playing eight-ball.
Mr Kass saw pool as a chance for Mr Obama to decompress after intense days in the Oval Office, and the two kept a running score. "He's a bit ahead," said Mr Kass, who left the White House at the end of 2014.
In those days, the President followed the billiards game with bedtime routines with his daughters.
These days, now that both are teenagers, he heads directly to the Treaty Room, named for the many historical documents that have been signed in it, including the peace protocol that ended the Spanish-American War in 1898.
"The sports channel is on," Mr Emanuel said, recalling the ubiquitous images on the room's large flat-screen TV. "Sports in the background, with the volume down."
By 8pm, the usher's office delivers the President's leather-bound daily briefing book - a large binder accompanied by a tall stack of folders with memos and documents from across the government, all demanding his attention. "An insane amount of paper," Mr Kass said.
Mr Obama often reads through it in a leather swivel chair at his desk, under a portrait of President Ulysses S. Grant. Windows on each side look out on the brightly lit Washington Monument and the Jefferson Memorial.
Other nights, the President settles in on the sofa under the 1976 Butterfly by Susan Rothenberg, a 1.8m-by-2.1m canvas of burnt sienna and black slashes that evokes a galloping horse.
"He is thoroughly predictable in having gone through every piece of paper that he gets," said Mr Tom Donilon, Mr Obama's national security adviser from 2010 to 2013. "You'll come in in the morning, it will be there: questions, notes, decisions."
To stay awake, the President does not turn to caffeine. He rarely drinks coffee or tea, and more often has a bottle of water next to him than a soda. His friends say his only snack at night is seven lightly salted almonds.
"Michelle and I would always joke: Not six. Not eight," Mr Kass said. "Always seven almonds."
The demands of the President's day job sometimes intrude. A 2011 photo shows Mr Obama in the Treaty Room with Mr McDonough, at that time the deputy national security adviser, and Mr John O. Brennan, then Mr Obama's counterterrorism chief and now the director of the CIA, after placing a call to then Prime Minister Naoto Kan of Japan shortly after Japan was hit by a devastating magnitude 9.0 earthquake. "The call was made near midnight," the photo's caption says.
But most often, Mr Obama's time in the Treaty Room is his own.
"I'll probably read briefing papers or do paperwork or write stuff until about 11.30pm, and then I usually have about a half-hour to read before I go to bed, about midnight, 12.30am, sometimes a little later," Mr Obama told Newsweek editor-in-chief Jon Meacham in 2009.
In 2014, Mr Obama told ABC's Kelly Ripa and Michael Strahan that he stayed up even later - until 2am, and waking up by 7am.
CAN YOU COME BACK TONIGHT?
His longest nights - the ones that stretch well into the early morning - usually involve speeches.
One night in June last year, chief speechwriter Cody Keenan had just returned home from work at 9pm when he heard from the President: "Can you come back tonight?"
He met the President in the usher's office on the first floor of the residence, where they worked until nearly 11pm on Mr Obama's eulogy for nine African-Americans fatally shot during Bible study at the Emanuel African Methodist Episcopal Church in Charleston, South Carolina.
Three months earlier, Mr Keenan had had to return to the White House when the President summoned him - at midnight - to go over changes to a speech he was to deliver in Selma, Alabama, on the 50th anniversary of Bloody Sunday, when protesters were brutally beaten by the police on the Edmund Pettus Bridge.
"There's something about the night," Mr Keenan said. "It's smaller. It lets you think."
In 2009, Mr Jon Favreau, Mr Keenan's predecessor, gave the President a draft of his Nobel Prize acceptance speech the night before they were scheduled to leave for the ceremony in Oslo. Mr Obama stayed up until 4am revising it, and handed Mr Favreau 11 handwritten pages later that morning.
On the plane to Norway, Mr Obama, Mr Favreau and two other aides pulled another near-all-nighter as they continued to work on the speech. Once Mr Obama had delivered it, he called the exhausted Mr Favreau at his hotel.
"He said, 'Hey, I think that turned out okay'," Mr Favreau recalled. "I said, 'Yes.' And he said, 'Let's never do that again.'"
SOME TIME FOR PLAY
Not everything that goes on in the Treaty Room is work though.
In addition to playing Words With Friends, a Scrabble-like online game, on his iPad, Mr Obama also turns up the sound on the television for big sports games.
"If he's watching a game, he will send a message. 'Duke should have won that game,' or whatever," said Mr Reggie Love, a former Duke basketball player who was Mr Obama's personal aide for the first three years of his presidency.
The President also uses the time to catch up on the news, skimming The New York Times, The Washington Post and The Wall Street Journal on his iPad or watching cable. Mr Love recalls getting an e-mail after 1am when Mr Obama saw a TV report about students whose "buc- ket list" included meeting the President. Why had he not met them, he asked. "'Someone decided it wasn't a good idea,' I said," Mr Love recalled. "He said, 'Well, I'm the President and I think it's a good idea.'"
Mr Obama and his wife are fans of cable dramas like Boardwalk Empire, Game Of Thrones and Breaking Bad. On Friday nights - movie night at the White House - Mr Obama and his family are often in the Family Theatre, a 40-seat screening room on the first floor of the East Wing, watching first-run films they have chosen and had delivered from the Motion Picture Association of America.
There is time, too, for fantasising about what life would be like outside the White House. Mr Emanuel, who is now the mayor of Chicago but remains close to the President, said he and Mr Obama once imagined moving to Hawaii to open a T-shirt shack that sold only one size (medium) and one colour (white). Their dream - that they would no longer have to make decisions.
During difficult White House meetings when no good decision seemed possible, Mr Emanuel would sometimes turn to Mr Obama and say: "White". Mr Obama would in turn reply: "Medium".
Now Mr Obama, who has six months left of solitary late nights in the Treaty Room, seems to be looking towards the end. Once he is out of the White House, he said in March at an Easter prayer breakfast in the State Dining Room, "I am going to take three, four months where I just sleep."
NEW YORK TIMES