^ Not really, no. AFAIK, when JFK spoke in normal day-to-day activities, his voice was more lower-pitched, like Bruce's was in the film.
Kevin Costner, OTOH, had one of the worst accents I've ever heard when he appeared in it. He sounded whiny and nasal. This accent is not easy to imitate - Andrew Robinson and Lane Smith absolutely nailed it in that 80's TZ episode, but not everybody can do it that well.