Reagan was the first of the useful idiot presidents (not fully cognizant but does what he's told) in the Religious Right movement that would become the white Christian nationalist takeover we're watching unfold today.
If he died in office (which was expected with his advancing Alzheimer's) George H. W. Bush would have taken over early, and while he wasn't dim, he was a total white Christian supremacist and a Nazi sympathizer.
As much as we like the idea of Earnest Hemingway shifting through time hunting the worst human beings ever to have lived, the awful reality is usually they were propped up by terrible circumstances.
This is certainly true regarding Hitler and Trump, and unless our plutocratic overlords can see to it that circumstances change for the better for the public we will see more Mussolini wannabes running for office.
Maybe assassinate Jerry Falwell, but make it look like an accident or FBI-drugged psycho-killer got him.
it was factions of the Republican elite who reached out to the religious right to get support for their neoliberal agenda, when they saw them successfully organise politically. Reagan happened to be of a similar religious leaning, but his reinterpretation of pre-existing American civil Christianity to these ends is much more than one of a useful idiot being told what to do.
source: this was a major part of my bachelor's thesis
Fools! With a time machine, I would go forward, and read history books, I want to know how it all turned out and what I could maybe do today, or in the recent past, that may make our future become a reality sooner, or make it better....
I may also go back and hand a big pile of gold to Nikola Tesla so he can keep doing his thing..... That man did so much science that ushered in the technology we use today, that I can't see anything bad happening if he were allowed to live his life in comfort, continuing his research for another decade....