I'd say Buchanan still wins. Saw the Civil War coming and basically stood back and let it happen. Was even sympathetic with slaveholders and the South in general even though he was from Pennsylvania.
But I hope to see the day sentiment finally changes and Reagan joins the worst Presidents list.
American presidents didn't stop or start genociding natives with Jackson.
Fun Fact: Grant assigned Sherman to figuring out how to genocide Indians in the most efficient way possible, leading to the buffalo extermination campaigns.
I know there's the argument that "Reagan lead to Trump", but I don't think that's particularly applicable. Also, Reagan's "legacy" as it where has had 40 some years to really seep in. Trump has only had 8, and even in just those 8 he's at the very least giving Reagan a run for his money.