I agree that this in an important issue (see Scot McKnight's thoughtful blog on this at www.jesuscreed.org). But I wonder if our belief that a presidential candidate's position on abortion is really going to make a difference is really valid.
True, it will make a difference in the appointing of Supreme Court Justices, although those Justices are free to change their minds along the way. But it isn't likely that either candidate will stop abortions in our country. I think that horse, so to speak, is already out of the barn. Once the courts have decided that removing a woman's right to choose an abortion violates the constitution, it will be very difficult if not impossible to change the law.
I once heard John Wimber say that we shouldn't be surprised at the embracing of abortion in our country. After all, he said, the world has always had an appetite for sacrificing its young.
So what are we to do if our candidates aren't likely to alter the course of these events? One of the early church fathers, in a debate with a non-Christian thinker, offered up an interesting contrast of the Christian community vs the pagan community. He observed that the pagans routinely aborted the unwanted unborn (a horrific thought in the 2nd or 3rd century) and also abandoned unwanted infants outside the city where the wild animals could consume them. Then he said, in essence, "We don't do that. In fact, we find your abandoned children and raise them as our own." Both Jews and Christians were known for taking in these unwanted infants. They couldn't stop the larger culture from disposing of their young, but they could do differently within their own communities.
I think this might speak to us. Regardless of the choices people are making, we don't do that. Perhaps we should first of all seek to reduce the number of abortions in our country by addressing the practice within our Christian communities. If people claiming faith in Jesus in the US refused to get abortions, the numbers would probably drop somewhat.
Perhaps being the light of the world and the salt of the earth begins with a commitment to do and not do certain things, regardless of the practices of the larger culture. In doing that, we shouldn't cut ourselves off from the world as though we are enclaves of untouchable holiness, but we should rather shine the light of life in the kingdom of God for the sake of a broken world.