I'm about to embark on what may be as important as an initiative as anything I do as President, trying to nudge the world in the direction of doing something serious about climate change.

Stamina. There is a greater physical element to this job than you would think, just being able to grind it out. And I think your ability to not just mentally and emotionally, but physically be able to say, "We got this. We're going to be OK."

It is time to leave behind the divisive battles of the past. It is time to move forward as one nation.

My administration will be the most transparent in history

Of course I have got concerns. Donald Trump and I differ on a whole bunch of issues.

When we helped prevent the massacre of civilians trapped on a distant mountain, here's what one of them said: "We owe our American friends our lives. Our children will always remember that there was someone who felt our struggle and made a long journey to protect innocent people." That is the difference we make in the world.

In a global economy where our economies and supply chains are deeply integrated, it's not even possible.