Based on true events
I have a wild fan theory that not only is back to the future based on true events, but that we are Biffs future.
I’m not sure if anyone’s made the connection before, but I believe Doc Brown to have been loosely based on Thomas Townsend Brown. Other than being called Dr. Brown, he is heavily connected to theories related to antigravity and time travel.
When Townsend Brown passed away, Trumps great uncle, John Trump, was in charge of going over all Browns work and finding anything that may be of use to the US government. Officially, he said there was nothing of relevance.
My theory, is that his uncle found research that lead him to be able to utilize time travel, and that he passed it down to the now president. Basically that we are now living in part two, when Biff is rich and famous and the rest of the world is an earthly hellscape.