Can a Catholic be for Barack Obama? The question has been raised by a law professor at Pepperdine University, who went from being a Mitt Romney adviser to an Obama supporter. The question is further raised by the appearance of the angry Rev. Michael Pfleger, a longtime friend of the Democratic nominee who recently preached at Obama's former Trinity church.

Since this topic was recently a matter of talking heads' concerns, I was asked, in all seriousness, if Catholics can even vote. After all, war is bad. The death penalty is bad. Abortion is bad. John McCain supports the war on terror and capital punishment, but he is against abortion. Obama is antiwar and anti-death penalty but pro-abortion. So neither wins. Or does Obama win? "Can Catholics vote for anyone?" readers asked.

The answer is not up to me. The individual Catholic derives an answer through reflection on the demands of his or her conscience, informed by the teaching of the Church. Neither of those steps can be glossed over. And there can be no mistaking what responsibilities the Catholic voter faces.

E-mailers have also asked, as the following did: "You are, of course, aware that the Catholic Church also sees contraception as a sin as well. Since means never justify the ends, voting for a candidate that promotes contraception as an alternative to abortion is also wrong. Without researching, I assume all major candidates have no problem with contraception, therefore, no candidate should get Catholic votes by your line of reasoning. I'm sorry for this rant, but I do not like people playing politics with my religion."

It is true that no presidential candidate is going to call for a ban on contraception. That's not a serious consideration. But politics can never be wholly divorced from religion. Our religious morality necessarily informs our political judgments.

Pope Benedict XVI, in a speech to European politicians in 2006, offered some instruction for the Catholic conscience: "As far as the Catholic Church is concerned, the principal focus of her interventions in the public arena is the protection and promotion of the dignity of the person, and she is thereby consciously drawing particular attention to principles which are not negotiable. Among these the following emerge clearly today: the protection of life in all its stages... recognition and promotion of the natural structure of the family... and the protection of the rights of parents to educate their children."

That "not negotiable" is not to be missed.

The thing about abortion is, it's not just any other issue. As serious as so many others are, abortion is not open to debate; it falls into the category of non-negotiable.

So can a Catholic vote for a politician who supports legal abortion? Providing guidance, Archbishop Charles Chaput of Denver writes that a Catholic voter would "need a compelling, proportionate reason to justify it. ... It's the kind of reason we will be able to explain, with a clean heart, to the victims of abortion when we meet them face to face in the next life -- which we most certainly will. If we're confident that these victims will accept our motives as something more than an alibi, then we can proceed."

The Catholic Catechism instructs that a child "must be treated from conception as a person." Obama said that he would never want his daughters to be "punished" with the birth of an unplanned baby, as if it were a thing to be disposed of. As an Illinois state senator, he opposed legislation that would protect babies born alive in botched abortion attempts. He explained, "Whenever we define a previable fetus as a person that is protected by the Equal Protection Clause or the other elements in the Constitution, what we're really saying is, in fact, that they are persons that are entitled to the kinds of protections that would be provided to a -- a child, a 9-month-old -- child that was delivered to term ... it would essentially bar abortions, because the Equal Protection Clause does not allow somebody to kill a child, and if this is a child, then this would be an antiabortion statute." That would be a child, albeit not a 9-month-old child, whose life he dismissed. This is the Democrats' candidate for president.

Catholics need to know what their Church teaches. Know your candidate. Know abortion isn't just any issue. It's a grave offense and betrayal to protecting the most innocent human life. If you're a Catholic who honestly can see how Obama's election as president won't contribute to or compound that offence, go in peace. I don't see it. I don't see how anyone can see it. And so for those who don't get a vote, for those who have been murdered in the name of "choice," this Catholic will cast hers against him in November.