BC, since you've thought this through so carefully, I'm sure you will be able to prove that liberals advocate the use of abortion as a form of birth control. I won't accept conservative nut-job sources that claim liberals advocate the use of abortion as a form of birth control, just as a warning. You'll have to prove it through mainstream liberal sources themselves.
It doesn't matter if one personally eschews abortion as a method of birth control but votes to allow others to make that choice without consequence, hindrance, or protection of the rights of the unborn to be born. If LDS doctrine is against such a thing, then one has voted contrary to LDS doctrine.
I'm still looking for an exclusively left wing issue/modus operandi that does not contradict LDS doctrine. It's telling that no one has listed one yet.