Missouri is the home of a number of conservative Christian denominations, and it is one of the most religious of states with major metropolitan areas in it. It has also seen the exodus of union jobs and, with it, the exodus of Democratic votes.
Yeah its pretty obvious was that there was a collapse in a share of the white rural democrat vote who voted for Trump. Meanwhile like in other states there was a increase of democrats from 2012 voting for Johnson or Stein in 2016 because they didnt like either candidate.
