There's a lot of evidence that providing aid and support for women, children and the poor, lowers the number of abortions. Pro lifers can choose to see present results rather than repeating exhortations for the future.
After all, to roll back and change laws in a democracy, the legislators, the courts and the majority of voters have to be convinced, and this process of moral reorientation on abortion can be a slow process. Think of the arguments you have with your friends and family.
In the interim, when immediate overthrow of a flawed law is impossible it is morally permissible, as John Paul II expresses it, to recognize "the art of the possible" and try to "limit the harm done by such a law."
Moreover, Catholic pro life advocates for Obama desperately want to limit the grave moral evils and dangers to life arising from pursuing preemptive wars, defending the use of torture, continuing the death penalty, and flouting of Constitutional and international law. As billions are spent on the destructive Iraq war, the needs of the poor, the ill and the schools are neglected, and the whole economic system falters.
Our Bishops have instructed us in the 2008 document "Faithful Citizenship," to inform our consciences and choose prudently. We must seek the common good as well as avoid evils. Bishops carry out their role of teaching and transmitting the tradition when they state Catholic social teaching in its fullness and nuance as they have here. And yes, if others in public life misrepresent Catholic doctrine, it is the Bishops' right and duty to correct them.
Moreover, in this document the Bishops firmly assert that they seek to inform consciences and "do not intend to tell Catholics for whom or against whom to vote." Yet certain Bishops (we know who they are) appear to be doing their best to coerce the conscientious decisions of their people by punitive uses of sacramental power. To deny Catholics the Eucharist because they have voted in a certain way seems to grievously overstep clerical authority as well as distort Catholic teaching on religious liberty.
While I think Obama is far and away the candidate most completely in agreement with Catholic teaching on peace and justice, I would never want to have McCain's Catholic followers be denied communion because of their votes on preemptive war or embryonic stem cell research.
In fact such non pastoral exercises of clerical power involving worship give scandal. This is imitating Jesus? Christ the Lord showed unfailing charity to all, even his enemies. He welcomes all who seek him.
Jesus teaches, heals, inspires and proclaims in one of my favorite scriptural verses, "Look, I have set before you an open door, which no one is able to shut."(Rev. 3:8)