Speaking now about the Apollo 11 flight, President Richard Nixon.
"Fate has ordained that the men who went to the moon to explore in peace will stay on the moon to rest in peace1... er..."
Two hours and a gigantic correction later...
Whew! At least that's the biggest mistake I'll make during my time as president!
1Safire, Bill. "In Event of Moon Disaster," National Archives and Records Administration, 18 July 1969, https://www.archives.gov/f iles/presidential-libraries/events/centennials/nixon/images/exhib it/rn100-6-1-2.pdf. President Richard Nixon prepared a backup speech in case the Apollo 11 flight failed.