This is a topic that can be very well informed by Catholic moral theology.
Catholic teachings are “non-negotiable.” For example, the sanctity of unborn life from the moment of conception must be held by all Catholics. Abortion is always an evil, and evil can never be accepted, even if it is intended to advance a good.
Cooperation with evil is a dicey business, but there are parameters for doing in a morally licit way. Cooperation with evil can be formal or material.
The distinction between formal and material cooperation is important. Formal cooperation with evil, that is, intentionally helping someone else conduct a sinful act, is always wrong. Material cooperation occurs when one’s participation in an act unintentionally helps another person do wrong. Material cooperation may or may not be wrong. It is important whether material cooperation is either proximate or remote.
Proximate material cooperation occurs when one’s actions are extremely closely related to the conduct of evil. For example, the German maintenance worker who was in charge of replacing empty poison gas canisters used in the showers used to kill Jewish people was not himself killing people, but his actions were closely related to the conduct of mass murder.
Remote material cooperation occurs when one’s actions are unintentionally and more distantly related to the conduct of evil. For example, the power company that provides electricity to abortion clinics might be providing a necessary thing to the conduct of abortion, but also provides power for all sorts of other beneficial uses.
Whether a person’s remote material cooperation with evil is morally licit depends on whether the person has a sufficient reason for their cooperation. For example, the power company employees’ provision of electricity for use in hospitals, traffic lights, and refrigeration units is necessary for saving many lives, preventing traffic deaths, and avoiding food wastage.
Voting is a tricky matter. A Catholic may not licitly vote for a candidate to promote abortion. That would be formal cooperation in evil. However, a Catholic may vote for a pro-choice candidate, presuming they disagree (and make clear their disagreement) with that candidate’s views on abortion, if there is a sufficient and serious reason for voting for them based on other factors (or “proportionate reasons” to use the wording of then-Cardinal Ratzinger’s leaked letter on voting from 2004ish).
In the current U.S. presidential election, it’s a big deal. Many pro-life Catholics want to vote for Donald Trump, because they see the open seat on the Supreme Court left by the death of Justice Scalia and desperately want to avoid Hillary Clinton naming a justice that may be as abortion-friendly as she is.
Personally, I am not sure how I’m going to vote. For sure, not for Trump.
I see Donald Trump as a danger to this country. Having disabled family members, his mockery of a disabled reporter was deeply offensive to me, as were his comments about Mexicans and treatment of women. I think his business record of aggressive litigation against rivals and opponents reflect a future trigger-happy commander-in-chief, and his choice of “bizarro” foreign policy advisors during his campaign doesn’t help (to cite the National Review). I am honestly afraid that he is going to pull us into a large-scale senseless war. I think his immigration policies will impoverish many families in Latin America that rely on remittances from the U.S. His economic policies seem a total disaster to me. He seems ready to blame the problems of the coal industry (much of which was brought by the low price of fracked natural gas) on regulations.
Though I do disagree with her on a number of issues (e.g., religious freedom, guns), Hillary Clinton is not as terrifying to me. She is undoubtedly pro-abortion and secular, but she’s riding on a culture of cheap contraception and redefined humanity – that’s something we need to fix through evangelism, not politics.
I have written a piece on how I think the pro-life movement needs to change, from my perspective as a health statistics professional. It’s here:
forums.catholic-questions.org/showthread.php?t=1014345
Though that piece wasn’t particular to this election, I can say that I don’t think overturning Roe v. Wade would make much of a difference in the overall abortion rate. As such, I do not believe that a vote for Donald Trump or Hillary Clinton would make a very big difference in abortion rates. I think Hillary’s desire to overturn the Hyde Amendment is horrible, and that could certainly increase abortion in America, but that’s a single policy battle still to face. Given the evidence I have seen that the government isn’t going to be the way to end abortion, I believe that a vote for Clinton from a truly pro-life Catholic could be considered remote material cooperation in evil, based on the all the other awful things I think Trump could to do this country and the world (i.e., war, poverty in Latin America, suppressing the economy).
I can’t honestly say whether I’ll vote for Clinton, or write in “None of the Above.” The Libertarian and Green Parties are both pro-abortion as well, so they’re right out. However, I just don’t want people to pretend that voting for Trump is a truly life-affirming vote.