I do agree with your point that we should look at a leader as a promoter of how a Ben noach should act (and not merely how he will do politically) that being said, I would like to make the following points:
1 abortion’s are osur for a Ben noach according to the Torah.
2 the same goes to same gender marriage.
It is clear that our job is to promote the 7 mitzvah’s (as the rambam rites)
Just another final thought, a republican wh will bring with it much more religious freedom.