Thoug not the same book, "Joshua, Son of None" was about a president being assassinated, and whom scientists cloned and raised with the same life the president had lived, in order to duplicate him not only physically, but in character. He grew up and ran for president. (Ending not given here.) The description so clearly matches John F. Kennedy. I am amazed that it didn't seem more popular.
(Also amazed that people assumed there have been no cloned people for the last 30 years. Though I don't know, I would not assume there are none.)
Not your book, but engrossing to read.)