The United States has been a global power since late in the 19th century.

Soviet foreign ministers would come in to see the president all the time, routinely. Jimmy Carter stopped that after the invasion of Afghanistan. Ronald Reagan resumed it in 1984, I think. And so the fact of a meeting like that I think is not that big a deal.

I mean, when you get down to very low numbers of nuclear weapons, and you contemplate going to zero, how do you deal with the reality of that technology being available to almost any country that seeks to pursue it? And what conditions do you put in place?

Power... Military success is not sufficient to win: economic development, institution-building and the rule of law, promoting internal reconciliation, good governance, providing basic services to the people, training and equipping indigenous military and police forces, strategic communications, and more of these, along with security, are essential ingredients for long-term success.

I think when it comes to the issues, I'd advise him to stick to the script. But, I mean, Donald Trump is going to have some very tough conversations and he's going to be talking about some very tough and complicated issues in all of the places that he visits.I think anytime a president does things that are humanizing, I think it's - it's good.

If possible, to be in a position to announce who is going to step in as the interim immediately. And if possible, to announce who you're going to nominate to replace that person. For that to be somebody of impeccable integrity and reputation disarms a lot of the worst criticism that it's some kind of a power play. It's a professional approach to replacing a senior official, which is always going to get a lot of attention.

There is no international problem that can be addressed or solved without the engagement and leadership of the United States and everybody in the world knows that, its just fact of life. So sometimes I think we could conduct ourselves with a little more humility.