Technically, the gathering this month was a fundraiser for Terry McAuliffe’s campaign for Virginia governor. But to those in attendance, it felt like a cozy family get-together. There, in the wood-paneled study of McAuliffe’s father-in-law’s Florida home, Bill Clinton stood with his arm draped around the shoulders of the candidate’s wife, Dorothy.

The former president waxed nostalgic about watching the McAuliffes’ five children grow into young adults, rattling off their names as he reminisced. He sounded more like a proud uncle than the political heavyweight who had flown in to hustle up money for their dad’s campaign.

Bill Clinton and Hillary Rodham Clinton have their own separate circles of personal friends and political advisers. But confidants say the McAuliffes are the rare individuals who cross into both spheres, part of a genuine friendship that is unusual at the highest level of politics.

The two couples are “as close to family as it can be without being blood, and it may even be blood by osmosis after all the time they’ve spent next to each other,” said John Morgan, a lawyer who co-hosted the Orlando area fundraiser for about 30 donors. “It has transcended friendship into love.”

Bill and Hillary, a potential 2016 presidential candidate, are leveraging their popularity in an all-out push to help McAuliffe win the governorship. On Sunday, Bill kicked off a four-day, nine-city tour of Virginia with McAuliffe, while Hillary will raise money for him this week in California.

“I love Terry McAuliffe — and his wife and his five kids,” Bill Clinton said Sunday night at a Hampton rally. “I’d be here if he were 50 points behind instead of about to be your next governor.”

The relationship carries political rewards and risks for both families. If McAuliffe wins the Nov. 5 election, the Clintons will have a trusted ally controlling one of the most important presidential swing states. But McAuliffe’s actions as governor would also reflect upon the Clintons, positively or negatively, far more than the actions of any other officeholder. McAuliffe’s history of using his deep political connections to benefit his private business portfolio would be put under a microscope again if Hillary Clinton runs for the White House.

Would McAuliffe, who has never held public office, emerge from the Clintons’ shadow or still be subordinate to them? How would he balance the interests of Virginia with the interests of the Clintons when they inevitably conflict? And would his legacy always be seen through a what-does-it-mean-for-Hillary prism?

“Terry is basically bought and paid for by the Clintons right now,” said Tim Miller, executive director of America Rising PAC, the leading Republican group attacking Hillary Clinton in anticipation of her 2016 campaign. “If Terry’s governorship is beset with scandal or any number of other things that happen, that’s going to have a real negative reflection on the Clintons.”

Miller said that a Gov. McAuliffe would stand as a reminder of the transactional relationships he helped nurture during the Bill Clinton presidency, when McAuliffe became one of the most successful fundraisers in political history. McAuliffe authored what became known as the “Lincoln Bedroom Memo,” which sparked controversy by offering special White House access to Clinton’s top campaign contributors.

In 1999, when the Clintons tried to buy a home in Chappaqua, N.Y., to establish residency for Hillary’s Senate campaign, they had so much legal debt they could not secure a mortgage. So McAuliffe put up $1.35 million of his own money as collateral on their loan. He was repaid once the Clintons obtained a conventional mortgage.

Miller suggested that the Clintons are campaigning so actively for McAuliffe as “a big payback.”

“That’s the way that the Clintons operate, in a very clubby, insider, ‘I scratch your back, you scratch mine’ D.C. manner,” he said.

Don Fowler, a former Democratic National Committee chairman who is close to the Clintons, dismissed that notion. “Every time that Bill Clinton has needed money, he’s called Terry, and Terry’s responded,” Fowler said. But he added: “I’ve never thought that there was anything nefarious or conspiratorial about their relationship.”

The alliance has been mutually beneficial, with McAuliffe rising to prominence in politics and business thanks largely to his ties with the Clintons. But people close to both families said in interviews that the relationship is rooted more in genuine friendship than in political or financial convenience.

Doug Sosnik, a political adviser in the Clinton White House, said the Clintons trust the McAuliffes because their connection is “not based on people wanting something from them — and that’s a problem that they’ve had.”

When Hillary Clinton formally endorsed McAuliffe at a Falls Church rally last weekend — her first political appearance since stepping down as secretary of state — she noted that the McAuliffe children “have been in and out of our lives as long as they’ve been alive.”

During Bill Clinton’s presidency, McAuliffe was at his side during the greatest triumphs and the lowest days. McAuliffe describes many of those moments in vivid detail in his memoir, “What a Party!”

On election night in 1994, when the Republicans won control of the House, it was McAuliffe who joined Clinton on the Truman Balcony to smoke cigars and ponder the thumping. It was McAuliffe who assured the president a week later, “They still love you out there.” And on election night in 1996, it was McAuliffe whom Hillary Clinton rushed toward with a bear hug when the networks called the race for Bill.

McAuliffe grew personally close to Bill Clinton as a fun-loving, hard-partying presidential sidekick. Confidants said Clinton is drawn to McAuliffe’s loud Irish humor and feeds off his endless optimism and energy. The duo frequently spent long nights in the White House residence playing cards and drinking (a beer for McAuliffe, Diet Coke for Clinton) and often played golf together.

After one sweaty round on a steamy July afternoon, McAuliffe wrote, Clinton invited him to use his personal shower. He played a practical joke on McAuliffe, leaving out a change of shorts that were three sizes too small. McAuliffe, afraid a butler might catch him, did a “panic search” through the president’s dresser drawers to find a pair that would fit.

During a trip to South Korea, Clinton and McAuliffe stayed up late in the president’s hotel suite sharing stories, McAuliffe wrote. After McAuliffe stumbled back to his room, a South Korean security agent asked one of his American counterparts: “Is there something we need to know about President Clinton? He was alone in his suite last night until almost 5 a.m. with a good-looking younger man.” The remark had Clinton and his aides busting up laughing.

Hillary Clinton described her husband’s relationship with McAuliffe as “a classical friendship,” saying in McAuliffe’s book that the White House is a lonely place and that it is rare to have “someone around whom you can be totally unguarded, totally open, totally trusting” with.

Over time, Hillary became close to McAuliffe as well. In 2008, when he served as national chairman of her presidential campaign, McAuliffe was one of her only traveling companions who, at the end of a frustrating day, could make Clinton laugh.

At the White House’s annual holiday parties, the Clintons and McAuliffes had a tradition: The president would dance with Dorothy, and the first lady would dance with Terry. The two families have frequently vacationed together as well, from weekends at Camp David and summers on Martha’s Vineyard during the White House years to more recent Christmases in the Dominican Republic. The families vacationed together as recently as summer of last year.

One exception was in August 1998, shortly after Bill Clinton’s affair with Monica Lewinsky became public, when McAuliffe’s plans to join Bill, Hillary and Chelsea were scratched when Hillary told him he couldn’t come.

But a few months later, McAuliffe went with the Clintons to Park City, Utah, for a weekend of skiing in celebration of Chelsea’s 19th birthday. “It was just the four of us and this was still a difficult, tense time for the family,” McAuliffe wrote, saying he was “trying to heal this family.”

This September, Hillary Clinton opened her Northwest Washington home for a McAuliffe fundraiser. As McAuliffe addressed donors in the back yard with Clinton looking on, she seemed to some attendees like a big sister pleased that her little brother had come into his own.

“It was just two good friends on the back porch,” said Morgan, the McAuliffe fundraiser, who was there. “I sensed from her, watching him, a great amount of pride.”