Not to get into a flamewar or anything, but if you're trying to prevent abortion then voting for the R candidate isn't a sensible choice. Hand in hand with wishing to ban abortion, they generally are hostile to the very policies (free birth control, such as IUD, on demand) that are the most effective in preventing abortion. Colorado cut teen birth rate and teen abortion rate in half simply by offering free IUDs[1].
The thing with the two party system is that the real choice for voters happens in the primaries. This is the chance to swing the party in a different direction, since in the general election people will typically hold their nose and vote a straight ticket even if they don't like all the positions their candidate holds.
[1] https://www.colorado.gov/pacific/sites/default/files/PSD_Tit...