"Feel free to kick us out," Hoffman recalled telling the president.
But Obama was just getting started. "I'll kick you out when it's time," he replied. He then lingered with his wife, Michelle, and their 13 guests - among them the novelist Toni Morrison, the hedge fund manager Marc Lasry and the Silicon Valley venture capitalist John Doerr - well past 2 am.
Obama "seemed incredibly relaxed," said another guest, the writer Malcolm Gladwell. He recalled how the group, which also included the actor Eva Longoria and Vinod Khosla, a founder of Sun Microsystems, tossed out ideas about what Obama should do after he leaves the White House.
"Where we'll end up, I don't know yet," said Marty Nesbitt, the president's long-time Chicago friend who is leading an extensive planning effort for Obama's library and an anticipated global foundation.
Publicly, Obama betrays little urgency about his future. Privately, he is preparing for his post-presidency with the same fierce discipline and fund-raising ambition that characterised the 2008 campaign that got him to the White House.
The long-running dinner this past February is part of a methodical effort taking place inside and outside the White House as the president, first lady and a cadre of top aides map out a post-presidential infrastructure and endowment they estimate could cost as much as $1 billion. The president's aides did not ask any of the guests for library contributions after the dinner, but a number of those at the table could be donors in the future.
The $1 billion - double what George W Bush raised for his library and its various programmes - would be used for what one adviser called a "digital-first" presidential library loaded with modern technologies, and to establish a foundation with a worldwide reach.
Supporters have urged Obama to avoid the mistake made by Bill Clinton, whose associates raised just enough money to build his library in Little Rock, Arkansas, forcing Clinton to pursue high-dollar donors for years to come. Including construction costs, Obama's associates set a goal of raising at least $800 million - enough money, they say, to avoid never-ending fund-raising. One top adviser said $800 million was a floor rather than a ceiling.
So far, Obama has raised just over $5.4 million from 12 donors, with gifts ranging from $100,000 to $1 million. The real push for donations, foundation officials said, would come after Obama left the White House.
Shailagh Murray, a senior adviser, oversees an effort inside the White House to keep attention on Obama's future and to ensure that his final 17 months in office, barring crises, serve as a glide path to his life as an ex-president. Obama's recent visit to a federal prison indicates, advisers say, a likely emphasis on criminal justice reform after he leaves office. His eulogy for one of nine African-Americans killed at a church in Charleston, South Carolina, is a forerunner, they say, of a focus on race relations.
"His focus is on finishing this job completely, thoroughly," said Valerie Jarrett, one of Obama's closest confidantes inside the White House. But officials in the West Wing said the president's thinking about some of his signature issues - including health care, economic inequality and fighting climate change - also involved considering their incorporation into his life after January 2017.
The heart of the post-presidential planning is Obama's own outreach to eclectic, often extraordinarily rich groups of people. The process started as early as the week after Obama's re-election in 2012, when the director Steven Spielberg and the actor Daniel Day-Lewis went to a White House screening of the movie Lincoln. Spielberg held the president spellbound, guests said, when he spoke about the use of technology to tell stories. Obama has continued those conversations, most recently with Spielberg and the studio executive Jeffrey Katzenberg over dinner at a Beverly Hills hotel in California in June, according to some of Obama's close advisers. The advisers said Spielberg was focused on helping develop a "narrative" for Obama in the years after he leaves office.
Among the debates at some of Obama's dinners: How could technology be used to provide global access to his presidential library? How prominent should Obama seek to be, especially in the first few years?
In response to a question from Doerr at the February White House dinner, the president told the group that he wanted to focus on civic engagement and opportunities for the youth, pushing guests for ideas about how to make the government work better, Hoffman recalled in an interview. The president asked if social networks could improve the way society confronted problems.
In their conversations with Obama and his advisers, people from Silicon Valley and Hollywood are pressing for a heavy reliance on cutting-edge technology in the library that would help spread the story of Obama's presidency across the globe. Ideally, one adviser said, a person in Kenya could put on a pair of virtual reality goggles and be transported to Obama's 2008 speech on race in Philadelphia.
Some discussions at the dinners have focused on the role Obama might play internationally after the diplomatic opening with Cuba, the nuclear deal with Iran, the confrontations with Russia and the draw-down of US forces in Iraq and Afghanistan.
In an interview on the website Tumblr last year, Obama was asked what he expected to be doing in 10 years. He took more than 30 seconds to respond, in a manner that suggested he had not yet settled on a good answer. "I haven't projected out 10 years," he said, offering his standard promise to remain engaged in policy-making until his last days in the Oval Office. "I know what I'll do right after the next president is inaugurated. I'll be on a beach somewhere drinking out of a coconut."
© 2015 The New York Times News Service