The Presidential election of 1876 was spectacularly fouled up.
Three states certified dueling slates of electors; Congress resolved the resulting confusion with a political compromise about the end of Reconstruction, and then passed laws to try to avoid a similar crisis in future years.
While we have been lucky since 1876 to not have another election with so many technical problems, the laws passed by Congress are not imperfect. Many of their nuances are very much alive today, and form a big part of the still-running dialogue about finalizing the 2020 Presidential election process.
To fully understand the end of this election, you need to channel "The Spirit of 1876" . . . .
(This PowerPoint presentation contains more information about the 1876 election and its consequences, prepared for a recent talk I did for a fundraiser for the New York City Urban Debate League.)