The Return of William Proxmire
A short story from my favorite SF author, Larry Niven. Basically, William Proxmire, in an effort to slash the space program for good, uses a time machine to go back in time and cure Robert Heinlein of his pneumonia while he's still in the Navy (figuring, without him writing sci-fi, most NASA people would never get interested in space).
However, when he returns to the present, he discovers that Heinlein (now an admiral) is the commander of the US Space Forces, has established a base on the Moon, and is on his way to Mars.
What I found pleasant about this was that (according to Niven) he sent this to Heinlein, who read it a week before he died.