34. Catholics often face difficult choices about how to vote. This is why it is so important to vote according to a well-formed conscience that perceives the proper relationship among moral goods. A Catholic cannot vote for a candidate who takes a position in favor of an intrinsic evil, such as abortion or racism, if the voter’s intent is to support that position. In such cases a Catholic would be guilty of formal cooperation in grave evil. At the same time, a voter should not use a candidate’s opposition to an intrinsic evil to justify indifference or inattentiveness to other important moral issues involving human life and dignity.
35. There may be times when a Catholic who rejects a candidate’s unacceptable position may decide to vote for that candidate for other morally grave reasons. Voting in this way would be permissible only for truly grave moral reasons, not to advance narrow interests or partisan preferences or to ignore a fundamental moral evil.
36. When all candidates hold a position in favor of an intrinsic evil, the conscientious voter faces a dilemma. The voter may decide to take the extraordinary step of not voting for any candidate or, after careful deliberation, may decide to vote for the candidate deemed less likely to advance such a morally flawed position and more likely to pursue other authentic human goods. –from Forming Consciences for Faithful Citizenship
