Follower's question:  I have heard that one of our past leaders, priest, bishop, cardinal, pope are on record saying that as a catholic we cannot support a political candidate that is not pro life. Can you tell me who that was and what was said and what the consequences of that was said to be?

Greetings! Thank you for this very important question. This question arises with some regularity, particularly within the United States, as the legal access to abortion and the defense of human life is consistently in the news.
 
Here’s what Cardinal Joseph Ratzinger (the future Pope Benedict XVI) wrote.
 
A Catholic would be guilty of formal cooperation in evil, and so unworthy to present himself for Holy Communion, if he were to deliberately vote for a candidate precisely because of the candidate’s permissive stand on abortion and/or euthanasia. When a Catholic does not share a candidate’s stand in favour of abortion and/or euthanasia, but votes for that candidate for other reasons, it is considered remote material cooperation, which can be permitted in the presence of proportionate reasons.
 
Ok. There’s a lot here! Let’s unpack it. First, Cardinal Ratzinger distinguishes between two types of “cooperation in evil,”—formal and remote material. Cooperation in evil is exactly what it sounds like; it’s when we do something that enables someone to do something that is morally wrong. Formal cooperation is when our actions make it directly possible for an evil action to occur. One example of this would be a nurse who assists in an abortion. Formal cooperation in evil is always forbidden. We can never do evil, even if our intention is to bring about something good. We commonly say, “The ends don’t justify the means.”
 
On the other hand, we have material cooperation in evil. This is when our assistance doesn’t directly help bring about some evil action. Sometimes this can be morally permissible, but not always. For example, a mail carrier could deliver mail to an abortion provider with a clear conscience. The provider simply happens to be on his or her normal mail route anyway. In truth, we all do this everyday. When we buy various products and pay taxes, undoubtedly some of that money goes to help pay for things we find morally objectionable. But, we are not expected to stop going to the grocery store or to stop filing our taxes. 
 
So, Cardinal Ratzinger distinguishes between these two types of cooperation in evil, and the distinction lies in our intention. Why are we voting for a politician who supports abortion? If it is because he or she supports legal access to abortion, then this is formal cooperation and is never morally permissible. If it is in spite of his or her support, and we would prefer that the candidate not support abortion access but we tolerate that support due to our agreement with the candidate on other issues, it is material cooperation and can be, but is not necessarily, morally permissible.
 
However, to participate, even materially, in some evil action, requires a proportionate reason. This is what Cardinal Ratzinger meant in the last line. Here’s an example. I know that when I buy a computer, some of that money will go to support things that are directly contrary to the Catholic faith, since the two major computer companies operating today (Apple and Microsoft) both support morally objectionable things. However, it’s not feasible in this day and age to live without a computer. It’s needed in my life and ministry. So, I’m not intending that the money I pay to Apple or Microsoft go to support things like abortion. But, I tolerate that support because I know I need a computer to do my work.
 
So, the question someone must weigh in determining whether or not to vote for a candidate who supports abortion is this, “Is there a proportionate reason present which justifies my voting for this person?” To answer this, it can’t be so simple as saying, “I agree with this person on tax policy, or immigration, or education, or welfare, or whatever.” And the answer’s difficulty is compounded because we can’t simply weigh up the good to be done and/or evil to be prevented and say, “Well, this outweighs that.” The reason we can’t do that is because it appeals to a philosophy known as “utilitarianism,” sometimes known as “consequentialism.” Essentially what this philosophy says is that we are to do the greatest amount good for the greatest number of people. In other words, we only look at the end result. And this is simply not consistent with a Catholic ethical view, because the ends don’t justify the means. We can never, ever, do evil in order to bring about a greater good. Ever. 
 
So, since allowing legalized access to abortion is intrinsically evil, meaning it is always wrong in every instance without any exceptions, to vote for a candidate who favors legalized access to abortion would require that his or her opponent favor an equally intrinsically evil position. Having a difference of opinion on taxes, or welfare, or immigration, or whatever, is not supporting something that is intrinsically evil. Catholics can have legitimate disagreement on these matters and still be within the scope of what is consistent with our faith.
 
So, all of that leads up to the answer. May a Catholic, with a good and clear conscience, vote for a candidate who favors legalized abortion? Yes, but it needs to be because that person’s opponent favors something that is equally intrinsically evil. Speaking practically, since the Roe vs. Wade decision in the United States, we have seen the slaughter of 60 million unborn babies. I would suggest that nothing, nothing, is proportionate to that.
 
Finally, consider this question from a different vantage point. Instead of thinking of abortion, substitute something else that is morally reprehensible, slavery for instance. Can any of us imagine saying, “I’m gong to vote for Candidate John Doe. I realize he favors legalized slavery, and I disagree with that, but I like him on everything else!” We rightly see the absurdity of such a position. The only reason we don’t see the absurdity with respect to legalized abortion is because the debate has been framed in such as way as this is seen as a right, and conveniently, those upon whom this “right” infringes, namely the unborn, have no voice in the debate.