With respect to Russia, my principal approach to Russia has been constant since I first came into office. Russia is an important country. It is a military superpower. It has influence in the region and it has influence around the world.

As a nuclear power - as the only nuclear power to have used a nuclear weapon - the United States has a moral responsibility to act.

It's time to "stop being ambivalent." ... They (groups like the Islamic State) have no ideology beyond violence and chaos and the slaughter of innocent people.

You may want to prove that you're worthy of other kids or neighbors who were wealthier than you and teased you. You may want to prove that you're worthy of high expectations. But I do think that there is a youthful ambition that very much has to do with making your mark in the world. And I think that cuts across the experiences of a lot of people who end up achieving something significant in their field.

If, technologically, it is possible to make an impenetrable device or system where the encryption is so strong that there's no key - there's no door at all - then how do we apprehend the child pornographer? How do we solve or disrupt a terrorist plot?

Here's the truth: even if countries like the United States curb our emissions, if growing countries like India - with soaring energy needs - don't also embrace cleaner fuels, then we don't stand a chance against climate change.

Look, first of all, the climate is changing. I don't think the science is clear what percentage is man-made and what percentage is natural. It's convoluted. And for the people to say the science is decided on, this is just really arrogant, to be honest with you, it's this intellectual arrogance that now you can't even have a conversation about it. The climate is changing, and we need to adapt to that reality.