Actually, the reason why Lincoln lost to Douglas had nothing to do with the debates (or philosophical/religious arguments above)... the Democrats controlled the IL legislature at the time, and they elected the Senators. Douglas was the Democrat incumbent, and Lincoln wasn’t going to be elected.
Senators were not directly elected at the time. The Senate battle was actually for the election of the state legislature. Thanks to Lincoln, the Republicans won a majority of the vote. However, due to gerrymandering of the districts, the Democrats won control of the legislature, and thus re-elected Douglas.
Exactly. The Illinois senate election was decided by the Illinois state legislators, not the voting public.