On the chaotic day that Joe Biden called Sen. Kamala D. Harris to ask whether she’d be his running mate, Los Angeles Mayor Eric Garcetti’s phone rang. As one of four co-chairs on Biden’s vice-presidential selection committee, Garcetti was one of a handful of people on the planet privy to that extensive and secretive process. On the other end of the line was someone even more involved in the decision: Joe’s wife of 43 years, Jill.

So central was Jill Biden’s role in the process that the selection committee had presented their initial findings to the Bidens as a pair. With Jill’s input, Joe narrowed the field of more than 20 to the 11 whom he then interviewed one on one. Joe called the other contenders to tell them Harris was his choice, and Jill was the one calling the four selection committee co-chairs to tell them the news.

The extent of Jill Biden’s influence on big decisions in her husband’s campaign to unseat President Trump is both mysterious and not. “It’s a marriage” is her standard line, which is to say, of course they’ve talked about this, they bounce things off each other all the time, and we don’t get to know the details. (Her staff declined to make her available for an interview.)

Here’s something we do know: The Jill Biden who will address the Democratic National Convention on Tuesday night is playing a far more active role in her husband’s campaign than she has in his past two White House bids, in 1988 and 2008, according to close friends and confidants. Though she’s spent eight years in and near the White House, her speech at the virtual convention will probably serve as a reintroduction to voters — a big moment for a potential first lady, even under these circumstances.

And what kind of first lady would she be? By all indications, a hands-on one. “I think she has a combination of Michelle Obama, Eleanor Roosevelt and Hillary Clinton,” said Randi Weingarten, president of the American Federation of Teachers, AFL-CIO, noting that all three were passionate about education but the latter two operated in the foreground, while Obama seemed more comfortable asserting her power behind the scenes. It’s likely Jill Biden would be a far more public and active first lady than Melania Trump.

Jill likes to tell the story of how in 2003, when party brass were at her house trying to get Joe to run, she marched past them in a bikini with “NO” written in marker on her stomach. This time, she’s pitched in on the campaign’s education unity task force, helping merge policy ideas from Sen. Bernie Sanders’s camp and her husband’s. She’s reached out to Hispanic leaders, trying to forge a tie with a group of voters that has been slow to warm to her husband. She has taken on routine but meaningful duties like informing Garcetti and other members of the vice-presidential search team of her husband’s pick, which was first reported by USA Today. At times, she’s even taken a turn as impromptu bodyguard, twice fending off protesters storming the stage while Joe was speaking.

With Joe largely campaigning from their home in Wilmington, Del., because of the coronavirus pandemic, she is the one who is physically with him on most days, while top advisers have scattered across the country. Family dynamics have changed, too, since the last time Joe ran for office — particularly after Beau Biden’s 2015 death of brain cancer at 46. Beau’s absence as his father’s confidant has left a vacuum that Jill has filled, according to friends.

And Jill herself has changed.

“When we started campaigning in 2008, she was a little nervous,” says Cathy Russell, Jill’s former chief of staff, who’s known and been working with the Bidens at different times since 1987. This time around, Russell was in Iowa for a month, sometimes meeting up with the former second lady as she maintained a packed schedule — often busier than Joe’s, according to staffers and outside observers. Jill would invite Iowa grandmothers out for wine and give her contact information to people who told her of sons dying of cancer or in the military. “She’s just really good!” says Russell, who recalled Jill going around to small crowds in rural towns trying to convince every reluctant voter individually. “She’s so much more experienced” 12 years later. (For all her effort, Joe Biden came in fourth in Iowa this year.)

The Iowa caucuses, too, feel like they were 12 years ago. Since then, Biden has managed to become his party’s nominee, and the situation in the country he’s trying to inherit has only become more dire. Beating Donald Trump is not Jill Biden’s job, but she’s made it clear that she intends to help her husband do it, and that she, too, is eager to get to work.

During the Obama presidency, Michelle Obama and Jill Biden traveled together as part of their Joining Forces initiative in support of military families, and the former first lady once described what it was like flying with her counterpart.

“Jill is always grading papers,” Obama said in their joint 2016 White House exit interview with People Magazine. “Which is funny because I’d forget, ‘Oh yeah, you have a day job!’ And then she pulls out her papers and she’s so diligent and I’m like, ‘Look at you! You have a job! Tell me! Tell me what it’s like!’ ”

Jill Biden had been a rarity: a second lady with a second gig. She was an English composition professor at Northern Virginia Community College (NOVA), a job she started in 2009, part of a long career in education that included stints at public high schools, at an adolescent psychiatric facility and at Delaware Technical Community College.

The enduring image former staff members repeatedly say they have of Jill Biden during the Obama administration is her carrying a stack of papers she had to grade on state trips to places like Israel, Japan or the Democratic Republic of Congo. One time, Jill asked to leave her office hours 10 minutes early, recalls Jim McClellan, NOVA’s liberal arts dean, because Joe was sitting in Air Force Two waiting for her to show up so they could do a three-country tour of Latin America. “I said, ‘Well, since the jet is revving up and using gas sitting on the runway, go ahead,’ ” McClellan says. She left with a stack of papers to grade and had them all done in time to be back in the office at 7 a.m. for her Tuesday classes.

If Joe Biden, who is 77, wins the presidency, Jill, 69, would not be the first first lady with an education background — Michelle Obama has been an associate dean of student services at the University of Chicago, and Laura Bush was a schoolteacher and a librarian — but she is among the most accomplished. Campaign and Obama-era staffers call her “Dr. Biden” in recognition of the doctorate in education it took her 15 years to get while raising three children — Beau and Hunter from Joe’s first marriage and Ashley, the daughter they had together. At NOVA, she works out of a cubicle and goes by the quasi-clandestine moniker “Dr. B.” (Her name isn’t listed in the course book.) When she had a Secret Service detail, she asked them to dress like students.

Her first year, she taught English as a Second Language and was so moved by her students’ stories that, according to McClellan, she’d write them on Post-it notes and leave them on the bathroom mirror of the vice president’s residency for Joe to read. Since then, she’s preferred teaching freshman composition and developmental English, which is meant to bring remedial students up to college writing level. Her reviews on RateMyProfessors.com, a website where users leave anonymous notes on college teachers, range from effusive — “literally my favorite professor” — to skull-and-crossbones-level warnings, all about her making them endlessly write journals and being a tough grader: “No sense of humor even though she tries to look nice.” “Be ready to writeeeee alotttttt !!”

This year’s campaign marks the first time she’s taken a break from teaching since she gave birth to Ashley in 1981. “She said she felt that if she didn’t give it her best shot, and that the election turned out not to be favorable to her husband, that she would regret not having done more,” McClellan says. Still, she’s attended voluntary training in online teaching and has said she intends to go back to NOVA even if Joe wins and they move into the White House. It would be the first time a first lady kept a day job outside the home, according to Anita McBride, who runs the First Ladies Initiative at American University and was Bush’s chief of staff. “This would be a precedent,” she says.

Education activists are practically giddy about the prospect of having Jill Biden in the White House, bending Joe’s ear. “They sit and talk about education issues over breakfast every morning,” says Lily Eskelsen García, president of the National Education Association, which is also Jill Biden’s union.

Weingarten, the American Federation of Teachers president, tells the story of how in 2010, a high school in Central Falls, R.I., fired all 93 teachers and staff members because of failing test scores — a move that President Barack Obama and his education secretary, Arne Duncan, backed publicly. Weingarten, who was vehemently opposed to evaluating teachers by test scores, says she had “a very heated discussion with the vice president,” who over the next few days got “very involved.” The educators were rehired later that year.

“He said to me, ‘I did my homework,’ ” Weingarten says, and she suspects Dr. B might have had a hand in that education. (The Biden campaign declined to comment on a personal conversation.)

Lately, Jill Biden has been chatting with lawmakers in the Congressional Hispanic Caucus over Zoom.

Joe has promised to pass comprehensive immigration reform in his first 100 days in office, and for six weeks beginning in April, Jill’s job was to listen while members of the caucus talked about their hopes for higher education and vented their frustrations with the 3 million deportations that took place under the Obama administration. Her placement on the issue seemed to signal how serious the campaign is about wooing their support. Jill is also working on learning Spanish via the Babbel app.

She’d take notes, said she’d convey their concerns to Joe and report back on her conversations with him at the next meeting. “And when we did meet with him on certain issues, he’d say, ‘Yeah, my wife, Jill, talked to me about that, and I’m all over it,’ ” says Rep. Tony Cárdenas (D-Calif.), who chaired the meetings. Every person who asked Jill to meet with their district got an immediate follow-up and usually saw her jump onto their Zooms that week.

As for Jill’s language skills, “It’s always kind of cute when somebody speaks Spanish and their accent is not as organic,” Cárdenas says, politely. Overall, “The big theme that emerged to me is that everyone was nodding their heads, saying, ‘I’m looking forward to working with her,’ ” he said. “She’s going to be a very active first lady.”

Jill was not a professional model like Melania Trump, but she did pose for local advertisements shot by a photographer friend, one of which caught the eye of 32-year-old first-term Sen. Joe Biden as he walked through the Wilmington airport in 1975.

As it turned out, his brother Frank knew Jill and gave Joe her number. The rest is history, which the Bidens have written themselves in their many books: Jill was about nine years younger, a tough-cookie “Philly girl,” the oldest of five girls who had once punched a bully in the face for throwing worms on one of her sisters. He was a widower who had lost his wife in a 1972 car crash that also killed his baby daughter and badly injured his young sons. Jill and Joe’s romance was a whirlwind, but it took five marriage proposals before she said yes; she’d been married and divorced young (“to a tall ex-football player who drove a fast yellow Camero,” she wrote in her 2019 memoir, “Where the Light Enters”) and she wanted to make sure, for the sake of Beau and Hunter, that this wouldn’t end in another divorce. She raised the boys, and they call her Mom.

Senate payroll records reviewed by The Washington Post also show that Jill worked as a “staff assistant” for four and a half months in Joe Biden’s office, from Sept. 10, 1975, until Jan. 25, 1976. This was before they married in 1977, and she used her prior married name, Jill T. Stevenson. It is not mentioned in her book and seems to be mostly lost from their biographical narrative. A Biden campaign aide downplayed her role, saying she was answering the phone in a front office when he was short-staffed.

A 1977 newspaper article says that a month after their wedding, she was still traveling once a week to work at his downstate office in between volunteering at a child abuse center and learning to play the piano. (Joe, laughing, said he’d had no idea she was working for him.) Jill didn’t speak for that article, either, and Joe asked for privacy on her behalf, telling Wilmington’s Sunday News Journal, “I don’t want to get her into the political thing.”

Tragedy struck again when Beau, an Iraq War veteran and former attorney general of Delaware, died in 2015 after two years with cancer. Jill, who lost her mother during the 2008 campaign, writes candidly about how grief changed her, describing herself as feeling “like a piece of china that’s been glued back together again” and saying that she lost her faith and stopped going to church.

“I thought at the time, and I still think now, that when she wrote it, she didn’t think her husband was going to run,” says Connie Schultz, a journalist and wife of Sen. Sherrod Brown (D-Ohio) who reviewed Jill’s memoir for The Post. The book came out in May 2019, a couple of weeks after Joe declared his candidacy. “If he had been planning to run, I have to believe there are people in the campaign who would have said, ‘I don’t think you want to be telling Catholic voters you no longer know what you think about God.’ ” (Jill told PBS’s Judy Woodruff that she’s regained her faith on the campaign trail.)

Jill Biden has become, in her own way, a vessel for other people’s grief just like her husband is. She stayed in touch with the woman who came up to her after Beau’s death in a nail salon and burst out weeping, telling Jill she was a Gold Star mother. The same year Beau died, Jill’s social secretary, Carlos Elizondo, lost his mother, and the Bidens hosted a memorial mass for her, with 100 of Elizondo’s friends, at the vice president’s residence. Her first communications director, Courtney O’Donnell, tells the story of how her husband had to have emergency surgery and spent 10 days in the hospital. One day, she left to take a shower and came back to find her sleeping husband covered in a new blanket with a tin of cookies by his bed. “I asked a nurse,” O’Donnell says, “and she said, ‘Oh, your boss came by. Sweet lady.’ ”

This year, perhaps more than ever, America feels broken and in need of gluing back together. Nearly 170,000 Americans have died in the coronavirus pandemic, and families across the country are facing all kinds of losses. Jill Biden’s empathy could give shape to her potential role as first lady beyond issue advocacy. In June, Jill flew with her husband to Texas to sit down with George Floyd’s family before his Houston memorial service. After an hour-long meeting, she gave her cellphone number to one of Floyd’s sons who was having a particularly difficult time, recalls Ben Crump, the Floyd family’s attorney. “She gave the number,” Crump says, “and said, ‘You call me anytime.’ ”

But before Jill Biden and her husband can try to make the White House empathetic again, they have to win an election that promises to be a knife fight. Trump is not above attacking the spouses of his opponents. He went after Ted Cruz’s wife, Heidi, for her looks during the 2016 primary and gleefully highlighted Bill Clinton’s sexual indiscretions during the general election. And while Trump hasn’t gone after Jill Biden yet, he’s made Hunter Biden a prime target.

When asked about Trump investigating Hunter’s work for a Ukrainian energy company while his father was vice president, Jill has appealed to unenforceable rules of decorum: “My family is not fair game. Joe is running against him. That’s different. Not my children,” she said on a CBS “Sunday Morning” special. (Hunter Biden is 50 and has made news before, opening up about his drug addiction, divorcing his wife of 23 years and having a romantic relationship with Beau’s widow while they were still grieving. Jill and Joe released a statement of support at the time. That relationship is over.)

When it comes to accusations of impropriety against her husband, Jill has carefully played the apologist. “I think it was a space issue. They felt like they wanted more space,” she said on the CBS special, addressing accusations from Lucy Flores, a member of the Nevada State Assembly, and six other women who’ve accused Joe Biden of inappropriate touching. “Joe realized that and learned from it.” On former Senate aide Tara Reade’s claim of sexual assault against Joe, which he has denied, Jill has remained silent.

When it comes to Joe’s former opponents, Jill has played a diplomatic role. Though she has said Harris’s attacks on Joe over school busing during a June 2019 debate “felt like a punch in the gut,” Jill reached out to Harris’s husband, Doug Emhoff, when Harris dropped out in December, wanting to convey that she understood how difficult and painful that decision must have been. Harris’s friendship with Beau when they were attorneys general in California and Delaware was also a key factor to her selection.

Jill has also had a collegial relationship with Jane Sanders, wife of Bernie Sanders, Joe’s foil on the left flank of the Democratic Party and someone whose voters he needs in November. Bernie’s fans don’t like Joe’s politics, but Jane likes Jill. “It was clear to me then, and it’s clear to me now that she’s a really decent human being and a person who lives by the creed, which I do, of ‘treat others as you would want to be treated,’ ” Jane Sanders said.

They texted back and forth throughout the primaries and were often seated together at debates because their husbands were often close together in polling. Jill struck Jane as a well-grounded person who genuinely cares about people. “Washington is not the most authentic place,” Jane said, “and when you find people that you know mean what they say and say what they mean, that’s something to treasure.”

Jane still wishes it was her husband accepting the Democratic nomination this week, of course, and says she and Bernie plan to keep pulling Joe Biden to the left on the issues; a former college president herself, Jane hopes to work with Jill on student debt and free college. (Jill currently supports free community colleges.) “Jill cares. She’s from a working-class background. That’s going to be good for America,” Jane said.

"This is odd," she said, "but I said to Bernie long ago, 'Wow, you know, I'd vote for you for president, but I think I'd vote for Jill as first lady if I had the option.' "

Correction: An earlier version of this story had several errors. Jill Biden's doctoral degree is an Ed.D, not a Ph.D. Jill Biden did not legally adopt Beau and Hunter Biden. Hunter Biden had a romantic relationship with Beau's widow, but they did not marry.

Matt Viser, Jenna Johnson and Michael Scherer contributed to this report.