Why would Obama, a man who ran a campaign based on an implicit rejection of the Clinton years, choose a symbol of those very years as his chief diplomat? Why would Clinton, a woman who is used to being the boss, agree to be a cog in the vast Obama machine?

For Obama, picking Clinton accomplishes practical and symbolic goals.

Practically, it’s hard to argue with her credentials or her readiness to represent the US in the world. Neither of the two other people considered for the job — New Mexico Governor Bill Richardson and Massachusetts Senator John Kerry — carried her star power, known and respected throughout the world.

Symbolically, picking Clinton sends a series of fascinating messages. It reinforces the “Team of Rivals” theme that seems to have transformed into conventional wisdom in the month or so since Obama was elected. Picking Clinton shows Obama’s bigness — that his pledge to bring in the best and brightest regardless of their past political entanglements is more than just lip service.

Bringing Clinton in board also serves as an example of the old adage that you keep your friends close and your enemies closer. Bill and Hillary Clinton were certain to be a base of power within the Democratic Party irrespective of whether they were actually part of the Obama Administration. By inviting them in through the front door, Obama is ensuring that he will have some control over America’s preeminent power couple.

But why did Clinton get into this? With the dream of becoming President deferred — certainly for a while, probably forever — Clinton had to decide how she wanted to spend the next 5-10 years of her life. She could be a top diplomat, a high-profile and influential force in the world community at a time when America is seeking to redefine its role and reposition itself. Or she could remain in the Senate, where her symbolic power as a national spokeswoman for the Democratic party occasionally conflicted with her decidedly junior status in the chamber.

It’s clear that Hillary Clinton believed she could have more impact in the former role.

In the end, that Obama and Clinton could stand together on a stage — one as president, the other as his secretary of State — speaks to the unpredictability and soap-operatic nature of politics. This is the beginning, not the end, of a fascinating storyline in American politics.