The past pulls out every weapon it has to keep Jake from reaching Dealey Plaza in time to save Kennedy. If he fails, it could mean death for Jake or others close to him. If he succeeds, it could create a world in which he loses everything he has ever known. What is the cost of doing the right thing?
When Jake goes back to 2016 the first time, a building in the distance has the words "Captain Trips" spray-painted on it. This is a reference to the disease that killed off most of the people on earth in Stephen King's "The Stand".