By Allison V. Smith, for USA TODAY On location: Stephen King spent a lot of time in Dallas at the 6th Floor Museum, where Lee Harvey Oswald fired the shots that killed JFK.
http://www.wbir.com/news/article/191319/141/Stephen-King-evokes-horrors-of-history-in-112263-
http://www.stephenking.com/promo/11-22-63/promo_page/
I am surprised someone hasn't written a time travel novel about the JFK assassination before this one. Maybe they have and I just don't know about it. I suppose many people have thought of writing a book about going back and trying to stop the assassination from happening.
If you did go back in time trying to stop the JFK assassination would be like a nightmare. The Secret Service would not believe you if you told them. They would just arrest you. And you could not get to the grassy knoll and the 6th Floor of the Texas Book Depository both at the same time.
Many unexpected things could happen to keep you stuck somewhere like in a dream making it unable for you to get to the scene on time.
If you tried to get the Secret Service not to take the bubble top off the limo they would ignore you since it was JFK that told them to take it off that day.
And certainly one good way to end the book would be for you to be shot by the Secret Service while attempting to stop the assassination. They could then get rid of your body and history could continue unchanged.