But he wasn't. Off to the side, behind a serving table, was a video camera. The white-gloved waitstaff didn't know the camera was there - or didn't care - because waiters stopped in front of it to put down a decanter of red wine, or pick up what appeared to be champagne.
The video was released Monday on the website of Mother Jones, an investigative magazine, and on it Romney made some controversial statements.
"There are 47 percent of the people who will vote for the president no matter what. All right, there are 47 percent who are with him, who are dependent upon government, who believe that they are victims, who believe the government has a responsibility to care for them, who believe that they are entitled to health care, to food, to housing, to you name it. And the government should give it to them. . . . These are people who pay no income tax."
People at the dinner were asking Romney questions like "Why is it bad to aspire to be wealthy and successful?"
Leder, 50, who has contributed more than $230,000 to Romney's campaign and to super PACs that support him, declined to be interviewed Tuesday but released a statement:
"I hosted a fund-raiser for an old friend in May. I believe all Americans should have the opportunity to succeed, to improve their lives, and to build even better lives for their children. I have supported people from both political parties who share this view and make it a priority, even though their ideas on how to achieve it may differ."
Sixers majority owner Josh Harris and CEO Adam Aron both declined to comment as well Tuesday, and the team issued this statement: "The Sixers have no comment on an event that was held completely independent of the team and in which the team was not involved in any way."
Here is some of what is known about Leder:
He just got divorced, and his wife wanted $200 million, which she contended was half of his net worth. What she ended up getting wasn't disclosed.
He is from Long Island, the father of three, and he rented a mansion in the summer of 2011 in the Hamptons, paying $400,000 for July, according to the New York Times. He had a party there.
It was a wild night, with techno music blasting, professional dancers in exotic costumes gyrating on pillars, and people swimming naked. The party earned a headline in the New York Post: "Nude Frolic in Tycoon's Pool."
Leder has been spotted in the Caribbean with Russell Simmons of Def Jam and celebrity stylist Rachel Zoe, prompting another Post headline: "Private Equity Party Boy."
In January, Leder complained to the Times about his image:
"I think the portrayal of me as having wild and crazy parties is absolutely incorrect. I spend a small percentage throwing some parties, attending some parties. I like music. I like to dance. But rather than reporting on how I spend 340 days and nights of my year, the media likes to report on the other 25."
Leder and college friend Rodger Krouse were working for Lehman Bros. in 1995 when they met with Romney and colleagues at Bain Capital. Romney's people were said to be unhappy because they had only doubled their money on a recent deal. Leder and Krouse, according to the Times, knew they were in the wrong business, gave notice, and opened their own private equity firm, Sun Capital, locating it in Boca Raton. Romney reportedly helped with their early deals.
Sun Capital operates like Bain and most other private equity firms: It borrows money, buys distressed companies, and tries to rehabilitate them. Sometimes people lose their jobs and companies go into bankruptcy.
When the turnarounds succeed, investors make money. People like Leder can reap huge profits and fees.
Among the 73 companies Sun owns, according to its website, are such well-known retailers and restaurant chains as the Limited, Boston Market, and Friendly's, which Sun recently took through bankruptcy.
Locally, Sun owns PaperWorks Industries Inc. in the Manayunk section of Philadelphia. PaperWorks manufactures folding cartons and other packaging.
Another local holding was Jevic Transportation in Burlington County, which Sun bought for $40 million in 2006 and shut down two years later, putting 1,500 people out of work nationwide. Jevic remains in bankruptcy.
According to a 2010 article in American Banker, Leder honed his entrepreneurial skills playing blackjack at the University of Pennsylvania.
The article says Leder taught himself card counting and raised a $10,000 "fund" from fellow students. He gambled that money in Atlantic City and used the winnings to pay his tuition. "I was pretty good with numbers and calculations," he said.
He told the Times in January that his father had wanted him to be a doctor but that he hated dissecting frogs in biology and chose another path. He said he started reading the Wall Street Journal at 12.
Leder said he typically sleeps two to three hours a night before waking up to answer e-mails. He might not be sleeping even that well this week.
Contact Michael Vitez at 215-854-5639 or email@example.com. On Twitter: @michaelvitez.
Contributing to this article were Inquirer staff writers Joseph N. DiStefano, Harold Brubaker, and John Mitchell.