It was a confident, relaxed and very focused Hillary Clinton I met up with in Moscow this week, her first trip to Russia since becoming secretary of state. She was there to help – as she calls it, "restart" – the relationship between the two super-powers. The relationship had become increasingly rocky during the final years of the Bush administration.

"I will be the first to tell you," she said to students at Moscow State University, "that we have people in our government and you have people in your government who are still living in the past … They do not believe the United States and Russia can cooperate to this extent. They do not trust each other and we have to prove them wrong. That is our goal."

On her agenda with the Russians: Iran, Afghanistan and missile defense. She expressed satisfaction with her closed-door meetings and told me she believes the Russians will support sanctions against Iran if there is proof that the Iranians are developing nuclear weapons.

Click here to see a video clip of this interview on "Nightline’s" website.  

While emphasizing the improvement in understanding between the two nations and urging mutual respect, she did not shrink from directly confronting areas of concern. She attacked head-on the thorny issue of human rights: "People must be free to take unpopular positions, disagree with conventional wisdom, know they are safe to peacefully challenge accepted practice and authority," she said at Moscow State. "That’s why attacks on journalists and human-rights defenders here in Russia is such a great concern, because it is a threat to progress."

Clinton is the only secretary of state in the past 60 years, besides Ed Muskie, who comes from a political background. Sometimes that helps, she told me. "I think it gives me a perspective. I’m able to put myself in the position of the leaders. Obviously in some settings it’s easier than others. But if you’re an elected leader, you have to care about politics, so when I’m talking to someone I can say I’m not a bureaucrat, I come from a political world, so I understand that this is hard, but here’s how we can do it."

Clinton appears to have an endless reserve of energy for a truly grueling schedule. She routinely begins her days before seven o’clock AM and ends them long after midnight. Veteran state department officials in Moscow told me they had never seen a more ambitious series of meetings in a shorter period of time. Consider Tuesday: a meeting with the Russian foreign minister, a series of meetings at the U.S. Ambassador’s residence, a meeting with officials at Boeing, a meeting with the Russian president and, as if that wasn’t enough, the opera. We joined her for the first two acts but we slipped out at intermission. Clinton hung in there until the bitter end.

I spent a good deal of time with Clinton during the campaign last year but have never seen her, well, dare I say it, quite so happy. There is a certain ease about her – an openness that was often missing in the past. We commiserated about what a pain it is to get your hair looking right on the road; she joked about having vodka shots "for America" at lunch with the foreign minister. She was, it seemed to me – in the midst of all the pressure of her job – relaxed. For this super-charged intellectual, Iowa was tougher than Moscow. Maybe it’s the difference between "running" for office and governing. Maybe it is simply a new stage of life for her.