First lady's second take
On such a highly scripted day, it is the most tantalising unknown. Not what words Barack Obama will address to a deeply divided nation to mark his second inauguration, but what his wife, Michelle, will wear for today's celebrations.
Whether the president delivers rhetoric that soars, it is near-certain that her sartorial choices will delight her admirers.
In outfit number one she will stand next to her husband on the chilly steps of the Capitol.
But for fashion-watchers, the main focus will be her choice of dress and designer for her second outfit of the day, as she takes to the dance floor at the glitzy evening balls to music by the likes of Alicia Keys, Smoky Robinson and Stevie Wonder.
That the first lady unveiled a new hairstyle with a fringe for her 49th birthday on Thursday only fuelled the anticipation.
For even as her husband's reputation has taken a pounding since the heady days after he first took office in January 2009, so Obama has transformed from the reluctant first lady into a flourishing one.
The wife who was initially unhappy about moving her young daughters to Washington and painted by some critics as an "angry black woman" is now one of the nation's most popular political figures.
And just as her husband will look to his legacy over the next four years, so will Michelle.
That means developing her initiatives on childhood obesity and healthy living through her Let's Move campaign on nutrition and exercise and her support for military families.
For a woman who embraced the term of "mom-in-chief" on the campaign trail, the greatest focus will be steering her daughters Malia, 14, and Sasha, 11, through the challenges of their teenage years in the spotlight of the White House.
"Entering her second term, all the unknowns and trepidation and awkwardness of stepping into this ill-defined yet demanding role have gone," Anita McBride, chief of staff for the last four years of Obama's predecessor, Laura Bush, said.
There have been suggestions of grander ambitions.
After her rousing speech at the Democratic convention and her starring role in her husband's re-election campaign, talk grew that she should build on her status as first lady to run for office herself - just as Hillary Clinton, the last Democrat to serve in that role, has done.
But Michelle Obama used a pre-Christmas interview to quell any clamour for her to enter politics, saying that she had learned from her husband's experience and lacked the patience for the job.
Tellingly, when asked what trait she deplored most in herself and others, she said a failure to compromise.
Today it can be easy to forget that the assured figure almost had to be dragged to Washington when her husband was first elected, after suggesting at one stage that she and the girls would remain in Chicago until the summer to finish their school year.
She viewed Washington as "Barack's world" and only reluctantly surrendered her job after he entered the presidential race.
Indeed, the Harvard-educated high flyer had always been the main breadwinner while her husband worked his way from community organiser through Illinois state politics to the national stage in Congress.
The rocky start culminated with the disastrous publicity surrounding her private holiday to Spain in August 2010 with her daughters and a group of friends, accompanied by a large retinue of security and staff.
The trip on the taxpayers' dime earned her comparisons to a "modern-day Marie Antoinette" in some quarters.
Obama will only just have passed her 53rd birthday when she leaves the White House. Friends expect her to return to Chicago to pursue her interest in public health, establishing a charitable foundation and possibly assuming a senior university or hospital role.
In the meantime, they believe she may also write a book on health, and focus on broader issues such as poverty.