During the finale of a busy Democratic convention where some high-profile Democrats spoke for only a minute or two, a full tribute video was dedicated to Beau Biden. Vice-presidential nominee Kamala D. Harris spoke of him at length. Pete Buttigieg honored him as a fellow veteran. Beau provided the virtual introduction to his father’s acceptance speech via a video of him introducing his father when Joe Biden accepted the vice-presidential nomination in 2008.

Beau Biden, who died of cancer in 2015 at age 46, has hovered over his father’s campaign since before it officially began, at times more present than those who are physically there. Joe Biden talks of Beau’s military service to underline his own connection with the military. He cites his son’s high opinion of Harris as a reason he chose her as his running mate. He points to his late son as a source of inspiration.

Beau Biden’s presence at the convention, where numerous speakers referred to him, also underscored how little the nominee speaks of his other children, Hunter and Ashley, by comparison. His oldest son died just five years ago; the wound remains raw, and it is part of the reason he did not run in 2016.

Presidential campaigns have rarely placed personal tragedy so squarely at the center of their message. But family, compassion, decency and loss are key to the picture of Joe Biden his campaign tried to paint this week, and they intersect in Biden’s account of Beau.

Some who know Biden say he saw himself in Beau, and he himself has said he imagined it was Beau who might someday be accepting the presidential nomination. “It’s all about what I think — my family thinks — Beau would be doing if he was still here and doing it,” Biden said while on a tour for “Promise Me, Dad,” his book about losing his son.

The video tribute that played shortly before Biden accepted the nomination Thursday included remarks from then-President ­Barack Obama at Beau Biden’s funeral, praised his record in the military and highlighted his work on behalf of children during his tenure as Delaware’s attorney general.

“He did in 46 years what most of us couldn’t do in 146,” Obama said in the eulogy shown on video. “Think about the day that dawns for children who are safer because of Beau, whose lives are fuller because of him.”

Beau Biden was also featured in a separate video about his father’s commitment to military families.

Beau’s prominence isn’t new for his father. On the campaign trail during the primaries, Joe Biden often explained his decision to run in 2020 by recalling a conversation he had with his son just before he passed away, when Beau asked him to promise he would be all right after his death. Biden says he knew what his son really meant was that he should not let grief push him out of public service.

“Beau inspires me every day,” Biden said Thursday night.

Harris’s presence on the ticket has made Beau Biden an even bigger part of the campaign. She was a colleague and friend of his, creating a link between her and the presidential nominee that is personal as well as political.

It was Beau who first introduced his father to Harris, prompting the former vice president to call her “an honorary Biden” when he announced his pick earlier this month.

“Ever since I received Joe’s call, I have been thinking about the first Biden I really came to know, and that, of course, is Joe’s beloved son Beau,” Harris said at the time. “Beau was the kind of guy who inspired people to be a better version of themselves. When I would ask him, ‘Where’d you get that?’ he’d always talk about his dad.”

To many in their circle, Harris and Beau Biden in the early 2010s seemed to be on parallel tracks to political stardom.

When Joe Biden resigned his U.S. Senate seat in 2009 to become Obama’s vice president, political analysts thought Beau would run to replace him and win easily. Instead, he sought reelection as attorney general; friends say he wanted to stay and finish a high-profile child abuse prosecution.

Beau Biden and Harris became colleagues when she was elected California attorney general in 2010. The two were about the same age, and they shared priorities such as child welfare.

While their states differed vastly, they were thrown together during a multistate lawsuit against five big banks in the wake of the foreclosure crisis. When many attorneys general wanted to settle, a group of four, including Harris and Biden, held out for tougher penalties.

Pressure mounted on them to concede. California had been hit hard by predatory lending practices, and Harris was under pressure to take what the banks were offering. With his father as vice president at the time, Biden’s role also faced intense scrutiny.

Pushed from all sides, they forged a bond, Harris said. “During the Great Recession, we spoke on the phone nearly every day, working together to win back billions of dollars for homeowners from the big banks that foreclosed on people’s homes,” she said Wednesday night.

Their staffers often traveled for in-person meetings in Washington. When Harris or Biden needed a sounding board, they often called each other.

“Everybody loved [Beau],” said former Massachusetts attorney general Martha Coakley, another member of the holdout group. “He was easy to work with, but he had a sense of purpose, too. He was very determined, very empathetic, and he was what we called a ‘good guy.’ ”

In the years that followed, Harris and Biden stayed close. When Beau Biden wanted to fundraise in the Bay Area, he called Harris first to make sure he wasn’t stepping on her toes. He also introduced her to his father, who would go on to swear her in as the second Black woman to ever serve in the U.S. Senate in 2016.

By then, Beau Biden had passed away. The night he died, his closest staffers made a list of 60 people who they felt should know first. Harris was one of them, and staffers remember she was deeply affected by the loss.

It was because of that history, according to people close to him, that Joe Biden felt blindsided four years later, when Harris aggressively challenged his record on busing and race in a Democratic debate. The heated exchange spurred animosity in Biden’s camp, and the former vice president said he had not been expecting the blow because “she knew Beau.”

In the ensuing months, the wound at least partly healed. Biden began the next debate by telling Harris to “go easy on me, kid.” They patched things up behind the scenes, and while some in Biden’s camp took convincing, Biden — who said repeatedly he needed to be “simpatico” with whomever he chose as his running mate — made it clear her relationship with his son was one reason he picked her.

“The truth is, there’s not a lot of people whose opinion I valued more than Beau’s. When I was deciding who to pick as my running mate, I thought a lot about his friendship with Kamala and the respect he had for her,” Biden tweeted this week. “I know he’d be proud of my choice.”

Beau Biden’s prevalence in his father’s campaign stands in stark contrast to the near-total absence of his brother, Hunter, who has become a frequent target for the Trump campaign.

President Trump and his allies have pushed an unfounded theory that Joe Biden, while vice president, tried to obstruct a corruption investigation of a Ukrainian energy company, Burisma, on whose board Hunter served at the time.

Hunter Biden said later that while neither he nor his father did anything wrong, he regretted that his role on Burisma’s board gave ammunition to his father’s political opponents.

The Biden campaign has largely tried to shield Hunter from the public eye during the campaign, though he and Ashley introduced their father Thursday for his climactic speech. Their remarks were brief, if heartfelt, and ended by presenting the video of Beau so he could “have the last word.”

Twelve years ago, Beau Biden stepped to the podium in person at the Democratic National Convention to introduce his father, who was accepting the vice-presidential nomination that night. Beau was headed to serve in Iraq soon after, so he asked the crowd to do him a favor.

“Because of other duties, it won’t be possible for me to be here this fall to stand by him the way he stood by me,” he said. “So I have something to ask of you: Be there for my dad like he was for me.”