The most fascinating and important relationship in the Obama cabinet -- between the president and Secretary of State Hillary Rodham Clinton -- also happens to be the one we know the least about.

Have these two former rivals for the presidency really made peace? How trusted an adviser is Clinton for the president? How has she adjusted, if at all, to the subordinate role?

The president says little about the nature of their relationship -- limiting it to the broad idea that he likes to be surrounded by the best and the brightest and Clinton fits that bill.

"I actually think that Hillary Clinton has been very much a team player," Obama told Post reporters and editors days before being sworn in as president -- pronouncing himself "extraordinarily happy" with her performance.

Clinton hadn't discussed her new job or her relationship with the president in any way -- until she sat down yesterday day for an interview with George Stephanopoulos on the ABC's "This Week."

Clinton, who never gives away much of her internal thinking to the media, was far from an open book in her sitdown with Stephanpoulos but did give some insight into why she took the job and what she thinks of the man she serves.

The former first lady recounted that when she first heard the secretary of state rumors she dismissed them as media hype, and, even when Obama first asked her about the possibility, she was reluctant to consider it.

What changed her mind?

"Ultimately it came down to my feeling that, number one, when your president asks you to do something for your country, you really need a good reason not to do it," Clinton explained. "Number two, if I had won and I had asked him to please help me serve our country, I would have hoped he would say yes." (We can't help but speculate: If Clinton had won the nomination is there any way she wouldn't have picked Obama for vice president?)

As for putting the nastiness of the campaign -- typified by the "3 a.m." ad that sought to raise questions about Obama's readiness to sit in the big chair -- Clinton insisted it is no longer relevant.

She said Obama would "absolutely" be ready to field a 3 a.m. call with an international emergency, adding: "the president in his public actions and demeanor, and certainly in private with me and with the national security team, has been strong, thoughtful, decisive."

While we tend to be slightly skeptical that everything is absolutely hunky dory between the two former rivals -- a campaign that personal that went on for that long is not so easily forgotten -- it seems clear that Clinton and Obama have found a way to work together without any of the sort of public back-biting that so many expected when the former New York senator was chosen for the Cabinet.

One senior Democratic aide familiar with the interactions between the two described the relationship as "surprisingly warm."

The strength of that relationship will be tested in the coming years as Obama and Clinton seek to find a way toward Middle East peace. Obama, so far, has struck a relatively hard line with the Israelis -- insisting that a two-state solution is the proper course forward.

One theory goes that Obama's willingness to play the "bad cop" (of sorts) is balanced out by Clinton's good cop; she and her husband, former president Bill Clinton, are among the most stalwart supporters of Israel in the American government.

Can Clinton and Obama continue to make their relationship work to the mutual benefit of both sides? It's one of the central questions of the first four years of this presidency. So far, so good.