You could call them the power couple of United States foreign policy ... or perhaps, the odd couple.
Secretary of Defense Robert Gates is a Republican insider who has served eight presidents but shuns politics. Secretary of State Hillary Clinton is a Democrat and one-half of perhaps the most political couple on earth. Historically, the country's Secretary of State and Secretary of Defense have often been at each other's throats, competing for budgets, political turf and influence. Clinton and Gates say their experience has been the opposite.
"We didn't get the memo about how we were supposed to be diametrically opposite on everything," Clinton said, as she and Gates sat down with "Nightline's" Cynthia McFadden, the only joint television interview the two have ever granted abroad.
Watch the full interview on "Nightline" tonight at 11:35 p.m. ET
Clinton and Gates have formed a rare and powerful alliance. They've joined forces to become two of President Obama's most trusted advisors. In Bob Woodward's recent book, "Obama's Wars," they are referred to as two of the "blocks of granite" -- standing firm in their push for the president to add more troops in Afghanistan. This week found the pair meeting with officials in Melbourne, Australia. It's their fourth trip together this year.
Before they began working together, they didn't really know each other.
"All I knew of Hillary was what I'd seen on TV," Gates said.
Clinton knew Gates from his testimony before the Senate Armed Services Committee, which Clinton served on while in the Senate.
Gates, she said, was a change from his predecessor, Donald Rumsfeld.
"This secretary would actually answer questions. He would express his opinion," she said.
Today, the two like to share laughs about being older members of the administration.
"We have what we call the Old Folks Caucus," Gates said. ... "We're the only ones that kind of pick up on our cultural allusions and our jokes and things like that."
For Gates, old age jokes belie serious questions about his retirement. He confirmed to "Nightline" that he plans to leave his post "sometime next year."
"There is a lure in senior positions in Washington that makes you want to stay. And I think it's important and empowering to be willing to leave," he said.
Gates' close working relationship with Clinton, meanwhile, has only added fuel to what has become one of the most buzzed about parlor games in Washington: Whether Clinton will take Gates' job when he does retire.
Asked what she would do if Obama offered her the job, Clinton played coy.
"I have made it clear that I love the job I have," she said.
Gates, for his part, said he believed Clinton could do his job but added that one of her "great strengths" was being a "spokesperson for the United States around the world."
"That's not the role of the Secretary of Defense," he said.
As the subject turned to politics, Clinton was more open about her disappointment over last week's midterm elections.
"I was very sad to see a lot of good people turned out of Congress for doing the right thing," she said.
For Clinton, the elections brought back memories of 1994, when Democrats took a beating in that year's midterm elections, two years after her husband, President Bill Clinton took office.