From a recent interview with Archbishop Charles Chaput at the Pew Forum:

[W]e Catholics serve Caesar best when we serve God first, and that means living our Catholic beliefs vigorously, faithfully and without apologies at home and in the public, at work and in the voting booth. We can't ignore the sufferings of the poor or the homeless or undocumented immigrants and then claim to be good Catholics. We also can't ignore the killing of unborn children without struggling to end that daily homicide -- not just through supportive social policies, but by changing the law.

The law not only regulates, it also teaches. The current law of the United States teaches that it can be acceptable to kill an unborn child. But it isn't acceptable; it never was and never will be. And Catholics can't make peace with this kind of deeply evil law without lying to themselves, lying to the believing community and trying to fool God. It doesn't work.

The rest of the interview is here.