Ronald Reagan, October 27, 1964, in a speech he wrote himself:
You and I have a rendezvous with destiny. We will preserve for our children this, the last best hope of man on Earth, or we will sentence them to take the last step into a thousand years of darkness.
Featured here, in a campaign video for Barr ’08:
The transcript of Reagan’s speech is worth reading, or there is a full recording here. This excerpt begins after he has calmed his nerves and said:
If we lose freedom here, there is no place to escape to.
I’m going for a walk in the thunder.