We estimate that once Iraq acquires fissile material - whether from a foreign source or by securing the materials to build an indigenous fissile material capability - it could fabricate a nuclear weapon within one year.
— John Bolton

If you took every nuclear weapon ever built at the height of the Cold War, lumped them together and blew them up at the same time, that would be one one-millionth of the energy released at that moment.
Phil Plait on the asteroid that killed the dinosaurs nuclear weapon quote

Somebody once said, Al Qaeda does not have a return address, so if they attack us with a nuclear weapon, what's the response, and to whom is the response? They're retaliation-proof.
— Irwin Redlener

If Iran becomes a nuclear weapon state it is the end of non-proliferation as we know it. If Iran gets a nuclear weapon you are likely to see Saudi, Egypt and other countries follow suit and we will bequeath to the next generation a nuclear arms race in the world's most unstable region.
— Liam Fox

I'm absolutely convinced that the threat we face now, the idea of a terrorist in the middle of one of our cities with a nuclear weapon, is very real and that we have to use extraordinary measures to deal with it.
— Dick Cheney