But who said it's possible for you to go back in time and save Kennedy?
You can't
If you had gone back to save Kennedy then Kennedy would have been alive when you were born
I think you are confused about what is fixed, Kennedy dying is fixed, Oswald is fixed, you going back in time would just be a story about how you failed to stop Oswald
Or put another way, Oswald could have been the time traveler, like bran was the time traveler
and this is why it gets tricky
if you go back and save kennedy... and he's alive when you're born... then you would have never needed to go back and save kennedy in the first place... so why would you have done it?
bran goes back to make hodor, but if in the original story, there was no hodor... then the whole story would have changed, because hodor wouldn't be some mindless fool carrying bran around and being a slave to the starks in the first place
terminator goes back to kill connor... kyle reese fukks his mom and makes jon... then who was the original jon before reese was his dad and who taught his mom to make him a leader
see where i'm going... time travel never works... unless you go with alternate realities... as in you go back to a different timeline and change it... but the original timeline is the same.. you just fractured off to a completely new set of time
which would also mean there's millions of us in different time and dimensions, all doing the exact same things, except when a time traveler goes back and fukks with it.... it's all crazy