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 strictly defined.
Since abortion and euthanasia have been defined by the Church as the most serious sins prevalent in our society, what kind of reasons could possibly be considered proportionate enough to justify a Catholic voting for a candidate who is known to be pro-abortion? None of the reasons commonly suggested could even begin to be proportionate enough to justify a Catholic voting for such a candidate. Reasons such as the candidate's position on war, or taxes, or the death penalty, or immigration, or a national health plan, or social security, or aids, or homosexuality, or marriage, or any similar burning societal issues of our time are simply lacking in proportionality.
There is only one thing that could be considered proportionate enough to justify a Catholic voting for a candidate who is known to be pro-abortion, and that is the protection of innocent human life. . . . READ MORE
Source: Statement of Bishop Emeritus Rene Henry Gracida on Voting for Pro-Abortion Candidates. Catholic Online Exclusive (catholic.org).