2020:
An interesting election, but FPTP prevents an interesting result
Donald Trump (R) 358
(Green Party) 180
James Buchanan (D) 0
Nobody really supports the candidate that was, at minimum, tolerant of slavery.
1856
James Buchanan (D) 133 (below 148 needed)
John Fremont (R) 125
Donald Trump (A) 38
Trump is refused the nomination of the Republican party, but finds a home among the Know Nothings for his fiery oration. The election is made more complicated, but Trump's offense against Buchanan is unable to dislodge Fremont from his home state.
Members of the "Opposition Party", proto-Republicans, in Congress strongly prefer Fremont over Trump. Trump seems to have a lack of understanding regarding the importance of the slavery problem. I would need to do deeper research on who would win in the house, but it seems possible for Buchanan or Fremont to win. The Senate is able to install John Breckenridge as Vice President pretty easily.
