A trivia footnote to the anniversary of the moon landing: As president, JFK ad-libbed only once when speaking before Congress. Delivering a special "second" State of the Union address in May 1961, Kennedy made his famous call for a man on the moon by decade's end. As I recount in White House Ghosts: Presidents and Their Speechwriters, Kennedy did not think the Congress reacted with particular enthusiasm to the challenge. So he made it more bluntly:
I believe we should go to the moon. But I think every citizen of this country as well as the Members of the Congress should consider the matter carefully in making their judgment, to which we have given attention over many weeks and months, because it is a heavy burden, and there is no sense in agreeing or desiring that the United States take an affirmative position in outer space, unless we are prepared to do the work and bear the burdens to make it successful. If we are not, we should decide today and this year.
(While he was not inclined to do it front of Congress, JFK was a skilled ad-libber -- most of his famous Berlin Wall speech was off the cuff.)