Success as a modern first lady calls for the gifts of a silent movie star: a larger-than-life glamour that radiates from the screen, an indefinable ability to capture the mood of the moment, and the ability to communicate with the public largely in semaphore. Jackie Kennedy, of course, was as if to the manor born; Hillary Clinton never looked comfortable being seen and not heard. Laura Bush overcame her shyness to master the art, but by then she was sidekick to a show nobody wanted to watch.
Michelle Obama is a natural. While Sarah Brown, a clever and determined woman, has grown steadily in confidence in her role as political spouse over the last 20 months, her American counterpart looked at ease from the start.
This week, Michelle Obama faced her first major challenge on the international stage. She may have passed her American screentests with flying colours, appearing on the cover of Vogue in her first month in the White House, but the delicate negotiations in London, against the backdrop of high-profile protest, posed a new test. With electorates newly suspicious of elites and worried for their future, the G20 leaders and their wives knew that every step taken meant walking on political eggshells.
Barack Obama and Gordon Brown have international interpreters and banks of microphones, policy pronouncements and footnoted treatises to help them deliver their messages loud and clear. Their wives, by contrast, have only clothes, body language, and the knowledge that their schedule of appointments, however painstakingly planned as non-political, will be minutely observed for clues written in diplomatic code.
The wives' every gesture - Sarah Brown making tea in a pot, Michelle Obama putting an arm around the Queen - is beamed around the world, but the images are accompanied by Chinese whispers, rather than direct quotes. An image of the first lady and the Queen chatting while both looking at the floor, was captioned in the media with the information that they "appeared to be discussing their shoes", although no one evidently heard their conversation.
Almost exactly a year ago, Carlamania swept these shores when Carla Bruni-Sarkozy dazzled court and country in an enchantingly formal wardrobe of made-to-measure Christian Dior couture. What a difference a year makes. What looked charming and delicious then would look Marie Antoinette-ish now.
Michelle Obama's first coup was in tuning her wardrobe to a pitch of sunny, homely optimism, rather than sparkling glamour. For most of the visit the sleek, dynamic shift dresses which have been a feature of her wardrobe were replaced by low-key outfits made up of skirts and tops in colours whose deliberate almost-mismatch lent them a casual tone: a blush-pink cardigan with a mint gingham skirt on Wednesday, a peacock-and-turquoise combination on Thursday. When she did wear a dress, it was styled not to look like one: the zingy lemongrass Jason Wu frock she wore on arrival was layered with a black coat and belt, while the monochrome Isabel Toledo dress chosen for the Downing Street dinner was disguised as a two-piece ensemble.
The sequinned cardigan and check skirt were bought from J Crew, a midmarket American retailer whose clothes the Obama family often wear; instead of changing accessories with each outfit, Michelle Obama wore the same double string of pearls throughout the visit. These are minor details, but ones which help fix the first lady in the public perception as "real".
On their daytime appearances together, it was noticeable that while Sarah Brown appeared dressed as if for a day at the office, in her dark, solid colours and opaque tights, Michelle Obama's feminine skirts and detailed cardigans gave her the air of a woman having coffee with friends. This was significant, because this tone of female comradeship came to be the defining feature of her visit: greeting cancer sufferer Trudi Cogdell and her daughters with the words "come on - big hugs"; presenting Sarah Brown and Samantha Cameron with volumes of nursery literary classics for their children; charming the Queen to the extent that the two women stood with their arms around each other; making a surprise visit to the Elizabeth Garrett Anderson girls' school.
Whether or not the blue Argyle cardigan with the sequin trim is chic is not the point here. (Even I can see that.) The success of this trip for Brand Michelle was not that the international public think of her as more beautiful, or even as more stylish, but that they like her more, they relate to her more, and they trust her more. Carla Bruni may have seduced every man she met last year, but this year Michelle Obama charmed us all.
