Some governments are prepared to give up elements of sovereignty to address the threat of global climate change.

I think it was going to be hard to work with Russians on Syria. There is some potential overlap between the U.S. and Russia in that the Russians don't want to see the Syria situation unravel to a point where they have to escalate their own involvement. But at the moment, I don't see the U.S. and Russia on the same page in Syria. Russia seems much more interested in consolidating government control over liberated areas. It seems to me that the U.S. and Russia are proving they can disagree for independent reasons in any number of theaters.

Jerusalem is a holy site for Jews, Muslims, and Christians. Israelis and Palestinians both lay claim to it as their capital. Jerusalem is the most sensitive of all the issues that need to be addressed in order to achieve a peace agreement between Israelis and Palestinians. But Donald Trump determined an important aspect of the United States' position towards Jerusalem before any agreement. Most of the rest of the world feels that it ought not to be dealt with first, that it ought not to be dealt with separately, and that it ought not to be dealt with unilaterally.

If the president Donald Trump had connected the Jerusalem question to some other positions, linking it to Israeli and Palestinian behavior or putting the Jerusalem statement in a larger context of U.S. policy, it could have potentially advanced the peace process. But I don't see how singling it out might help.

Hillary Clinton is pretty much what we would call a foreign-policy realist, someone who thinks the purpose of American foreign policy should be to adjust the foreign policies of other countries, work closely with traditional allies in Europe and Asia towards that end.

I've worked for four presidents, and I've concluded that almost nothing is inevitable. History is to a significant extent the result of the interaction of personalities and ideas. And so I don't believe war between the U.S. and China is in any way inevitable, and it's well within the province of diplomacy and statecraft to avoid it.

I think what Mr. Trump has made clear is that he would not undertake optional wars, what I have called wars of choice, a la, say Iraq in 2003 or Libya, for the purposes of transforming another country. It's not clear whether Hillary Clinton, if she were to have the opportunity, would do such a thing again or whether she would have taken a - the lesson from both Iraq and Libya that we ought not to be undertaking those kinds of wars of choice.