I’m not sure how much Darwin followed politics in general and how interested he would have been in the USA elections. I do know that it takes up a lot of time and nervous energy for those of us living outside of the USA (and I can only imagine how it dominates inside America).
For Darwin, deep in the writing of the Origin, the 1856 USA election was between the Democrats (James Buchanan), the newly formed Republicans (John Fremont) and the fantastically named Know Nothing Party (Millard Fillmore). All three won states and Buchanan had a sizeable victory (although a few states were only won by a few thousand votes). Buchanan, pro-slavery, went on to help the country slide into the Civil War. I’m sure that Darwin had at least a passing interest in all of this (given his the strong abolitionist vibes of his family).