The Day of the Dolphin (1973)

"Unwittingly, he trained a dolphin to kill the president of the United States."
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Dr. Jake Terrell, who has been training a pair of dolphins for many years, has had a breakthrough. He has taught his dolphins to speak and understand English, although they do have a limited vocabulary. When the dolphins are stolen, he discovers they're to be used in an assassination attempt. Now he is in a race to discover who is the target, and where the dolphins are, before the attempt is carried out.

George C. Scottas Dr. Jake Terrell
Trish Van Devereas Maggie Terrell
Paul Sorvinoas Curtis Mahoney