Is there any document (catechism, canon law, etc.) or statement from a pope, bishop, etc., saying definitively that Catholics may not vote for pro-abortion candidates?
In his letter titled Worthiness to Receive Holy Communion, then-Cardinal Joseph Ratzinger (now Pope Benedict XVI) stated:
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 favor 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 (emphasis added).