Purse-lipped Washington etiquette experts have tutted at the informality of it all, but the Obamas have always been keen to appear accessible, even if the stand-offish reality is somewhat different.
The Obamas are the world’s most scrutinised couple at the best of times, but it will be rare to find a guest at the bash who won’t be secretly watching them with particular interest.
After all, the last time they were pictured together — at Nelson Mandela’s memorial — the First Lady was looking none too pleased as the her husband posed for a ‘selfie’ photograph with the leggy blonde Danish Prime Minister, Helle Thorning-Schmidt.
Indeed, if the U.S. tabloids are to be believed, the relationship of Washington’s golden couple is facing problems that go far beyond dirty looks.
Under the headline Obama Divorce Bombshell!, the National Enquirer claims their 21-year marriage has dissolved in a string of ugly fights that were prompted by the Mandela memorial incident and — far more outrageously — Mrs Obama’s discovery that Secret Service bodyguards had been covering up infidelity on her husband’s part.
It’s an allegation the White House has declined to comment on, though after Bill Clinton’s trouser-dropping scandals, Americans would be rather less sanguine about any extra-marital activity than the French appear to be over President Francois Hollande’s behaviour.
Mrs Obama, the Enquirer claims, intends to stand by her husband until his presidency is over, at which time he will move back to Hawaii, where he grew up, and she will stay in Washington with their children.
For the moment, they are allegedly sleeping in separate bedrooms after Mr Obama’s attempt to ‘mend fences’ backfired so badly on a recent Christmas getaway to Hawaii that he returned to Washington with their two daughters, leaving his wife behind.
The National Enquirer, it must be said, quoted only anonymous insiders in support of these sensational claims, and is hardly the most reliable source of hard news.
Obama advisers are certainly not talking as if there is any scandal in the offing.
The couple are ‘role models for parents all across the country’, according to old friend and adviser Valerie Jarrett. ‘She’s at the top of her game. She’s fabulous at 50.’
Washington’s media has ignored the story.
But everyone remembers how the Enquirer famously got it right when it claimed the supposedly squeaky clean Democrat presidential contender John Edwards had fathered a love child by a former campaign worker.
Thin as its story may seem at the moment, might it be on to something again?
At least it was right on one point — Mrs Obama did remain in Hawaii. The White House quickly offered an explanation, saying the extended stay had been a birthday present from her husband.
‘If you have kids, you know that telling your spouse they can spend a week away from home is actually a big present,’ said his spokesman.
Before returning home on Wednesday, Mrs Obama holed up for more than a week at TV star Oprah Winfrey’s spectacular 12-bedroom house on a mountainside estate on Maui, the second largest of the Hawaiian islands.
Their girls-only get-together was joined by Oprah’s close friend, the TV presenter Gayle King, White House aide Valerie Jarrett and Sharon Malone, wife of the U.S. Attorney General Eric Holder.
Oprah has described the estate as a place where she and guests sit on the porch sipping guava cocktails, and ride horses to the top of the mountain to watch the sun go down.
Why would anyone rush back to chilly Washington from such an idyll?
But if the rumours are true, and there were more painful reasons for Michelle’s reluctance to rejoin her husband, this would not be the first time such tensions have apparently surfaced.
Since he was elected President, two books have claimed the couple came close to splitting in their early years together, with Mrs Obama even drawing up divorce papers after deciding his burning political ambition was ruining their chances of domestic happiness.
In 2009, veteran Washington reporter Richard Wolffe claimed that the marriage almost collapsed nine years earlier because of Obama’s political drive and the family’s shattered finances.
‘There was little conversation and even less romance. She was angry at his selfishness and careerism; he thought she was cold and ungrateful,’ wrote Wolffe.
At the time, Mrs Obama had only recently become a mother — their daughters Malia and Sasha are now 15 and 12. Her husband, whom she had met while they were both working for a Chicago law firm in 1989, was a mere State Senator in Illinois who had just been thrashed in a battle for a seat in Congress.
‘She hated the failed race for Congress in 2000 and their marriage was strained by the time their younger daughter, Sasha, was born,’ wrote Wolffe in Renegade.
Wolffe noted, though, that they seemed to have got over their past issues by the time they made it to the hite House.
‘We’re going to be fine,’ he quoted Mrs Obama as saying. ‘We’re strong enoughto take anything on and be OK at the end.’
Yet, according to some accounts, Mrs Obama didn’t take well to Washington life.
Former French First Lady Carla Bruni revealed in a book how she had asked what life was like there. ‘Don’t ask! It’s hell. I can’t stand it!’ Mrs Obama reportedly told her. Mrs Obama later insisted she had never said that.
In 2012, meanwhile, political writer Edward Klein claimed Mr Obama had become so depressed about his failing marriage in 2000 that friends feared he was contemplating suicide.
Mrs Obama had been furious because she had warned him not to fight the disastrous Congress election battle which he lost, said Klein.
‘During the dark days that followed his defeat, he turned to Michelle for comfort. But she was in no mood to offer him sympathy,’ wrote Klein, who claimed Michelle’s friends told him she had even drawn up divorce papers.
‘He had dashed Michelle’s hopes of creating a stable and secure future,’ he wrote.
‘As a result their marriage was on the rocks, and Obama confided to friends that he and Michelle were talking about divorce.’