I can think about what [Mahatma] Gandhi said or [Martin Luther] King said about violence begetting violence, and still be true to my job by asking myself the question whenever we're confronted with a situation where some may be arguing for military action: Will this actually result in America being safer, or the most lives being saved?

The issue of climate change is one that we ignore at our own peril

What is required of us now is a new era of responsibility - a recognition, on the part of every American, that we have duties to ourselves, our nation, and the world, duties that we do not grudgingly accept but rather seize gladly, firm in the knowledge that there is nothing so satisfying to the spirit, so defining of our character, than giving our all to a difficult task. This is the price and the promise of citizenship.

Even limited military actions end up carrying with them great costs and unintended consequences.

I think my most important advice is to understand what are the foundations of a healthy democracy and how we have to engage in citizenship continuously, not just when something upsets us; not just when there's an election or when an issue pops up for a few weeks. It's hard work.

The United States does not have a monopoly on crazy people. It's not the only country that has psychosis. And yet we kill each other in these mass shootings at rates that are exponentially higher than anyone else. Well, what's the difference? The difference is that these guys can stack up a bunch of ammunition in their houses, and that's sort of par for the course.

If you're reading something from a Nobel Prize-winning physicist next to some guy in his underwear writing in his basement, or his mom's basement, on text, it looks like it's equally plausible.