Chick was leaning in to hear Bae tell the story of the mother and the lost son. She had put her pencil down. “It’s weird I’m going to go from this to being back at school,” Chick said. “It’s hard to explain all this to my friends.”

“You can’t,” Bae said.

“I never thought about how powerful a letter was.”

“Did you even know we had a correspondence office before you came here?” Bae asked her.

“I had no idea.”

“You think you’re going to be the mail lady or something.”

“We’re in the mailroom.”

“The mailroom.”

On a whiteboard was the countdown: “You have 99 days to make a difference in the life of a letter writer,” referring to Jan. 19, 2017, the last day of the Obama administration and the last day for this O.P.C. staff, nearly all of whom were political appointees and would no longer have a job at the White House. The election was less than a month away, and Donald Trump was still trailing Hillary Clinton by 8 points, according to the polls. “Our time is, like, ticking,” Bae told me. “We want to put our letter-writers in good shape for the next administration. We want them to be in good hands.”

Presidents have dealt with constituent mail differently over the years. It started simply enough: George Washington opened the mail and answered it. He got about five letters a day. Mail back then was carried by foot, or on horseback or in stagecoaches — not a high volume. Then came steamboats, then rail and a modernized postal system, and by the end of the 19th century President William McKinley was overwhelmed. One hundred letters every day? He hired someone to help, and that was the origin of O.P.C. It wasn’t until the Great Depression that things got especially tricky. In his weekly fireside chats, Franklin D. Roosevelt began a tradition of speaking directly to the country, inviting people to write to him and tell him their troubles. About a half-million letters came pouring in during the first week, and the White House mailroom became a fire hazard. Constituent mail grew from there, and each succeeding president formed a relationship with it. By the end of his presidency, Nixon refused to read anything bad anyone said about him. Reagan answered dozens of letters on weekends; he would stop by the mailroom from time to time, and he enjoyed reading the kid mail. Clinton wanted to see a representative stack every few weeks. George W. Bush liked to get a pile of 10 already-answered letters on occasion. These, anyway, are the anecdotal memories you find from former staff members. Little hard data exists about constituent mail from previous administrations; historians don’t focus on it, presidential libraries don’t feature it; the vast majority of it has long since been destroyed.

President Obama was the first to come up with a deliberate and explicit practice of 10 letters every day. If the president was home at the White House (he did not tend to mail when he traveled), he would be reading constituent mail, and everyone knew it, and systems were put in place to make sure it happened. The mail had currency. Some staff members called it “the letter underground.” Starting in 2010, all hard mail would be scanned and preserved. Starting in 2011, every email every day would be used to create a word cloud, its image distributed around the White House so policy makers and staff members alike could get a glimpse at what everyday Americans were writing in to say.

Dear Mr. President, [ ... ] YOU, sir, are the PRESIDENT of the United States. YOU, sir, are the one person that IS supposed to HELP the LITTLE PEOPLE like my family and others like us. We are the ones that make this country what it is. You say that jobs are up and spending is up. YOU, sir, need to come to my neck of the woods and see how wrong that is. Because here in Spotsylvania County, it’s not. I live in Partlow, a rural community of Spotsylvania, and I tell you what ... jobs are few and far between. My husband and I just want to be able to live and be able to buy a cake or a present for our kids when it’s their birthday or for Christmas. That’s another thing — my boys didn’t even have a Christmas because we did not have money to buy them presents. Have YOU ever had to tell your girls that Santa isn’t coming to your house? [ ... ] Sincerely,

Bethany Kern

Partlow, Va.

So much of the mail in the beginning of Obama’s presidency was about economic hardship and helplessness. There was a feeling of dread about climate change, and a loss of faith in everything from government to banks to the Catholic Church. Here was the new guy who said he could fix things. It was the getting-to-know-you phase. They told him their problems. They told him to quit smoking. They told him, wow, a black guy in the White House. They told him to get Bin Laden. They told him to create jobs. “Let’s see if you’re as smart as we hope you are.”

The tone of the letters was the main difference that Annmarie Emmet, a volunteer and a retiree, told me she saw. She read mail all through most of Bush’s two terms in office, then stayed on. “With Bush it would be more like, ‘Why aren’t you helping these people as a group, or doing more for that group?’ As opposed to personal struggles. I would say they felt a more personal connection with the Obamas. Kind of like, ‘I’m like you were, I need your help.’ And then from the beginning the L.G.B.T.Q. people have flocked to him. You never saw that in the Bush administration.”

Dear Mr. President, (Because the person I love can be dishonorably discharged for loving me back, even though he is honorably serving his country right now in Iraq, I have to send this letter anonymously. It pains me to have to do so.) [ ... ] My partner is currently serving in Iraq, and is in a situation where he is under fire on a daily basis. He’s a good soldier, and our country needs him to continue doing the excellent job that he has been recognized for. The day he deployed, I dropped him off far from his base’s main gate, and he walked alone in the dark and the rain to report for duty. Where the rest of his buddies were surrounded by spouses and children at mobilization ceremonies, he stood by himself. The phone trees don’t have my name on them, and base support services don’t apply — even though we’ve been together for 16 years and are raising a beautiful child together. Our communication is self-censored, and we are cruelly unable to nurture each other at the exact moment we both need it the most. If something were to happen to him, no one from his unit will call me. If, like so many good soldiers before him, he gives that last full measure of devotion, no one will come knock on my door. No one will present me with a flag. It is, and would be, as if the most important thing in his life — his family — never existed. [ ... ]

In 2009, Natoma Canfield, a cancer survivor from Medina, Ohio, wrote in detailing her staggering health insurance premiums, a letter Obama would keep framed and hung in a corridor between his private study and the Oval Office. “I need your health reform bill to help me!!! I simply can no longer afford to pay for my health care costs!!” It stood in for the tens of thousands of similar letters the mailroom was handling on the health care issue alone. They saw spikes in volume after major events like the mass shootings in Newtown, Conn., and Charleston, S.C.; the Paris terrorist attacks; the government shutdown; Benghazi. You could see it in the word clouds. “Jobs” might grow for a time, or “Syria,” or “Trayvon,” or a cluster like “family-children-fear” or “work-loans-student” or “ISIS-money-war” surrounding a giant “Help,” the most common word of all. After a gunman opened fire on police officers in Dallas last year, the word “police” ballooned, surrounded by “God-guns-black-America” with a tiny “peace” and even tinier “Congress.”