Part of what makes me most optimistic is if you look at the attitudes of young people. Across the board, young people are much more comfortable with respecting differences. They are much more comfortable with diversity.

Over more than a decade, Iran had moved ahead with its nuclear program. And before the deal, it had installed nearly 20,000 centrifuges that could enrich uranium for a nuclear bomb.

It is true, I worry about the hype. The only person more over-hyped than me is you.

Now, in practice, in daily social interactions, etc., there may be all kinds of biases and prejudices that are unspoken, that people aren't aware of, that affect who's hired, and who gets loans, and how kids are treated in school. But it's a powerful thing if you have on your side an idea that the overwhelming majority of people believe in because that's how you can build a consensus that's lasting.

I have seen, the desperation and disorder of the powerless: how it twists the lives of children on the streets of Jakarta or Nairobi in much the same way as it does the lives of children on Chicago 's South Side.

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.

We can't just drill our way out of the energy and climate challenge that we face.