Well, probably I would not have a problem with it. If I cared enough about it I might inquire what the evidence is to see whether it was credible. But it's like any other historical fiction, isn't it? You take a real figures like Abe Lincoln and maybe give him a mistress or a fondness for moonshine or have him meet secretly with Robert E. Lee to play poker. Why not? If you are publishing something as fiction you don't usually have to fill it with footnotes and prove everything you have said actually happened. It's fiction. (Sorry to irritate whoever it is that gets irritated by that statement.)
Well, okay. But I would expect a lot of people who care about Lincoln and/or American history to have a problem with it.
In fact, they tend to. Usually, when someone writes some preposterous work that's heavily revisionist in its history, you can usually count on established historians to hit the morning news shows and denounce it all as bunk.