Archbishop Chaput might consider the parable of the Roman Coin a little deeper.
There were two parties trying to trip Jesus up. The Herodians and the Pharisees -- neither party was acceptable to Jesus. Likewise, neither [John] McCain nor [Barack] Obama offers Catholics a legitimate "culture of life" agenda. While the archbishop continually harps on Obama's record on abortion, he ignores John McCain's dismal record on a multitude of other aspects of Catholic Social Doctrine.
I have been solidly against abortion my whole life and made career sacrifices as a result, but I do not think Chaput's refusal to dialogue with the other side offers the way to change.
We should attempt to find common ground, address the issues that put women at the mercy of men who force them to abort their children, address the inequities that drive women to despair where they see abortion as the only way to escape further harming their other children, and to work toward a world where abortion is no longer an option in the hearts and minds of people. That is a true path to change.