Barack Obama: “A terrorist attack with an improvised nuclear device would cost an enormous amount in terms of human life.”

When we choose, when we make that decision, I do believe – and there is evidence for this – that the world gets incrementally better, and that is a worthy goal and it’s worth fighting for.

A drift towards extremism was "not inevitable

I think when we act on that basis, it doesn't always work out, but over time things do get better.

It is a decision about how do we face and embrace this finite amount of time we have on the planet.