OK, here is a hypothetical scenario. Suppose we are living in some future time when the abortion laws are already quite strict - Life imprisonment for both the doctor and the mother and anyone who assisted in the operation. Now along comes a candidate who says that it is unfair to subject the mother to that harsh a punishment, since she may have been coerced, and is in favor of reducing the mother’s penalty to one year in prison, with early release possible based on individual circumstances. I think it would be proportional in that case to vote for the candidate who favored those particular “liberal” laws.
Of course that is not the situation we find ourselves in now, but it is still worthwhile to mention this scenario as it illustrates how the voting decision, at least in principle, can be dependent on political realities and is not so absolute as some would have us believe. And we in the Catholic Church know what it means for something to be absolute. It means it is true for all times and places. For example, I could never come up with a scenario under which abortion itself is OK. That is an absolute.
So let’s look a little closer to a realistic scenario, given today’s political realities. Suppose a candidate happens to be pro-choice, but he is running for an office in which abortion is never an issue, such as the Commissioner of Parks and Recreation. How would I know, then, of his pro-choice position? Well, suppose the candidate happens to be my neighbor, and we got to talking. If I thought that his opponent had an agenda for the park system that was bad for our town, I think I could vote for my neighbor, even if his opponent was more likely to be pro-life.
Another situation might be where the political realities are such that my vote for a pro-life candidate could be reasonably expected to make no difference in actual abortion policy. Of course we can never know for sure when a vote might make a difference, so we can’t say that it won’t make a difference with absolute certainty. But I think the probabilities of success are a relevant factor in deciding such an action.