"A Massachusetts Yankee in King Arthur's Court", Alternate Kennedys, edited by Mike Resnick, Tor, 1992, reprinted in We Could Do Worse, edited by Martin H. Greenberg, Dove Audio 1999, is a short fantasytime travel story by Harry Turtledove. It is an homage to Mark Twain's A Connecticut Yankee in King Arthur's Court, depicting US PresidentJohn F. Kennedy's brief trip to ancient Britannia, where Kennedy visits the court of King Arthur. Unlike Twain's work, the Camelot of Turtledove's story is a gritty and unromantic place, based on the real world of the 6th century and not on the magical realm of legend. Happily for Kennedy, magic isn't completely unknown.
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"Hail! Hail!", another story about historical figures - in this case, four of the Marx Brothers - traveling into the past.